Daniel@preciousmetalswest.com

 

 

Precious Metallurgy     

Table of Contents

Elements and Metals. 3

Copper-Cu. 3

Silver-Ag. 3

Zinc-Zn. 3

Nickel -Ni 3

Palladium-Pd. 4

Gold-Au. 4

A New Element.. 4

Manganese-Mn. 4

(Not Very) Secret Ingredients. 5

Silicon-Si 5

Boron-B.. 5

Cobalt-Co.. 5

"Grain Refiners". 5

Why do grain refiners not respond well to the small shop torch caster?. 5

Fuel, Oxygen, Metallic Chemistry.. 6

Reaction of gold with air. 6

Reaction of silver with air. 6

Reaction of copper with air. 6

Reaction of zinc with air. 6

Why do argon, nitrogen, and forming gases help castings come out clean?. 6

Hydrogen Torch Melt Of 24kt.. 6

Torch Fuel Gases. 6

Natural gas. 6

Acetylene. 7

Propane. 7

Hydrogen. 7

The Argument for Hydrogen-The #1 element. 7

Chemical reactions of the gaseous elements and combustion.. 8

Reaction of hydrogen with air. 8

Reaction of carbon with air. 8

Some important safety notes about fuel gases for torch casting-. 9

Cooking With Electricity.. 9

Making Electrons Work for You. 9

Resistance melting. 9

Induction melting. 10

The Alloy Story-The first mix of metals and heat.. 12

Balancing Act. 12

Casting Alloys. 12

Fabrication Alloys. 12

Induction. 13

Alloy Content  Chart. 14

Yellow Gold. 14

Green Gold. 15

White Golds. 15

Some electric machines struggle to melt white gold. 15

White gold either really white or really soft never both. 15

Rose Golds. 16

Sterling Silvers. 16

Exotic Colors Of Gold.. 17

Purple. 17

Blue. 17

Black. 17

Brown. 17

Bottom Line.... 17

Credits & Gratitude. 18

Properties of Natural Gas and Propane. 21

Using  Precious Metals West alloys. 21

Metal. 21

Dowse. 21

Melting. 21

Oven Controller Chart.. 23

Basic Precious Metallurgy Issues

Addressing the implications of  alloy behavior and jewelry manufacturing practices.

 

Many of us need a better understanding of just exactly what effect different base metal elements have on gold. Each base metal (really elements, found in the periodic table) that goes into making  alloy for karating has its own effects. The silver we add to most alloys complicates the equation considerably. Not to mention the host of deoxidisers, flow enhancers, and the grain refiners.

 

We depend on good behavior from our alloys. Soft when needed for setting or bending, then strong later to stay in shape or firmly hold a diamond in place. Bright finish, and above all no surprises! Just where do all those good and bad behaviors come from? Largely from the ingredients we need to make alloys. So, that's where we start.

 

Elements and Metals

 

Copper-Cu

One of the oldest metals known to man and the most common ingredient in gold alloys. The only red metallic element we have. Copper has the effect of helping every ingredient mix well. It faithfully reacts or alloys with almost anything. This is a mixed blessing. To the good, copper allows us a huge range of behavior and color control. The down side is oxidation, O2 reacting with Cu to cause all kinds of trouble. The new de-ox or non tarnishing silver mixes all eliminate or at least minimize the copper content by using other elements. When grandmas silver tarnishes, it's really the copper content in the sterling doing the damage. When we increase the amount of  copper in an alloy, the color goes to the darker/redder side. So, this is what we use to make rose/pink/red gold. Copper happens to be the largest ingredient in brass, which is simply copper and  zinc. The melting  temperature is 1984.32 Fahrenheit

 

Silver-Ag

 The next most common alloy element is silver. This ancient element has the wonderful ability to make up for many of the difficulties copper causes. Silver softens the mix for easier setting or bending. It also lightens the color toward the green-yellow side. Silver is the most common element to make green gold. It is a "grain refiner", that is to say in most circumstances we get smaller (better) grain structure with silver than without it. Silver is used in yellow & rose golds, and sometimes in white gold. Very little silver is used in nickel white gold, many white gold alloys contain no silver at all. Palladium white gold does use a lot of silver. Silver of course is used in early all alloys for gold. The melting  temperature of silver is 1763.2 Fahrenheit

 

Zinc-Zn

Zinc was first discovered as a separate element  in 1500, in Germany. Its use in brass goes back to ancient times. If we use only gold, and silver and copper, we get less than desirable color in 10k & 14kt. Too dark for many clients. We also get high casting temperatures. The element we look to for this fix is Zinc. Notice that the most common yellow metal around us by far is brass. Brass is usually about 70% copper and 30% zinc. When an alloy is yellow it improves the color of 10kt. From one perspective, yellow alloys can be seen as a high quality brass with silver added to keep the mix soft & the grain size reasonable. This white, soft, low melt element really saves the day in 10 & 14kt Yellow, some nickel white alloys, and even in some light rose color alloys. If overheated, zinc vaporizes off as a white smoke. This causes upward "karat creep". Zinc does oxidize, but is not nearly as troublesome in that way as copper. Soldering is a challenge for the same reason.  The melting  temperature is 787.15 Fahrenheit The boiling temperature is about 1100 F, which shows why some prefer non zinc alloys.

 

Nickel -Ni

This very white, very high temp metal is the color ingredient in white gold. Most jewelers do not realize that nickel white alloys are really mostly copper! The nickel is the source for white color, but at a cost. It is the source of the things we dislike in white gold, like high melt temperatures and hardness. The melting  temperature of nickel is a whopping 5275 f! Nickel white gold is very hard compared to other colors. Due to a perceived health risk, it is not allowed in some European retailers. Europe decided that enough people are nickel sensitive to restrict the amount of nickel dissipation allowed from any jewelry. Very few alloys can pass this test, and some people got sick from alloys that passed the test!.  This is ironic when you consider that nickel was discovered in Sweden in 1751.

 

 

 

Palladium-Pd

Discovered in 1803 in England this maybe the best alternative to nickel for making white gold. Usually mixed with a lot of silver and sometimes a bit of copper (remember how copper helps behaviors like blending and strength?) On the up side, palladium white is very soft. On the down side- High temps, and relatively poor color unless a very high (at least 45%) palladium mix is used. The actual melting temperature of palladium is 2830.82 Fahrenheit Nickel is the white color king I'm afraid. Notice that palladium percentages can run in excess of 50% while with nickel we usually see 15% to 25% in the alloy without the gold. Plan on rhodium plating any palladium white gold.

 

Gold-Au

Gold of course is the element we depend on most as jewelers. Gold is fairly well understood by jewelers world over, so we will keep this section short. This ancient metal is what we are adulterating if you will, with all the alloys we use day in and day out.  The melting temperature is 1947.52 Fahrenheit Nothing else in the world has the true color of gold.

A New Element

Manganese-Mn

This element may be a good substitute for nickel. PMWest has a nickel free white alloy that uses manganese and most of the above elements to make a "Euro-friendly" white gold. We soon  discovered that the best thing about this alloy may be its soft nature once mixed into our alloy.

 

This is an alloy that contains no nickel or palladium whatsoever. This means that there will be no nickel related problems such as skin sensitivity, 1900+ degree casting temps or nickel silicate, or SO2 related porosity. The high expense and  casting temperature of palladium is avoided completely.

 

We know it rolls to a 70% reduction before annealing, we know it fills castings like no other white gold in the world. We also know it flows at 1600 degrees Fahrenheit, way below nickel or palladium whites, and even lower than many yellow gold alloys!. Oddly enough despite record low casting temperatures when alloyed, the melt temperature of this element is 2275.0 Fahrenheit

 

We began casting in 2000. Our tests were performed using hydrogen torch vacuum casting and a Memco inducto vac that we own. Marc Robinson first cast the new white gold. He developed the procedures to use the alloy. Robert Lumabao, our shop foreman-another expert caster- uses a hydrogen torch to cast.  Further tests were conducted by a large local customer in Los Angeles on a Neutec J10. Memco did some in house casting for us. Everyone struggled the first few casts, then got it down

 

Instructional materials were produced and we began shipping two formulations in 2001.

 

I must admit the faults as well here. The bad news items are an extreme sensitivity to oxygen, and temperature control. Manganese tries to become slag or gas off causing porosity. Many early casting were overheated by customers who set the flow temp way too high, or the same as for nickel white, like 1050 C! Karating is the most difficult task. Casting is then easy. Machining and polishing goes well. You need a lot of flux, borax/boric based to solder. Kiln soldering failed early tests with base metal solders, typical for making chain on a large scale. Concast tubing is being made. The resulting tubing is machined into bands. Nickel free solders are now available. We had to make these solders to go with the new gold. However, if you want to size a palladium based nickel free ring, you need the new solder! .  One real problem is that this material will not solder cleanly in a conveyor belt oven furnace. In theory these things solder in an oxygen free atmosphere, but even trace oxygen ruins this delicate alloy.

 

I began casting with this gold to get my own feel for what customers were reporting to me. I don't cast much. I almost never cast at the same place twice. Working closely enough to cast with the clients while sorting  out their production difficulties is quite an education.

 

It is easy to cast or roll, if the printed instructions are followed to the letter. The alloy has been tested in hydrogen torch casting and in casting machines that can use a hydrogen/nitrogen mix to protect the gold from the air.  Continuous casting works very well for this alloy, it may in fact be a better fabrication alloy than anything else. The real challenge comes with getting used to manganese. This element which is very light, and very reactive with oxygen. The less oxygen, and the best temperature control is what works well.

 

The color is very good, comparable to most nickel based alloys and superior to some. Rhodium is appropriate to prevent time tarnishing and to improve color.

 

These white golds are very soft. This will please stone setters and fabricators the world over. Tubing, pave setting, very thin gold wire or sheets are all feasible. Kiln soldering is still being investigated. Early results were not helpful, but developing new powdered solder will help.

 

The "00" white gold is very easy to melt, the temperatures are similar to yellow gold. This is a crucial advantage for casters who use resistance melting.

 

(Not Very) Secret Ingredients

 

Most of the following ingredients are used by alloy makers to make your work easier to accomplish.

 

Silicon-Si

A deoxidiser, that allows us to re cast old gold with moderate amounts of new gold added. This stuff protects to a great degree from oxidation and from investment/gold reactions. The downside- larger grain structure than we would really like. Once again, this solves one set of problems, but creates some trade offs.

 

Boron-B

A reputed deoxidiser, this really helps offset the poor effects of silicon. Nearly always found in alloys containing silicon to offset the above mentioned thick flow.

 

Cobalt-Co

Used in certain proprietary/patent alloys to increase hardness after heat treating. Very effective when used correctly.

 

 

"Grain Refiners"

These elements are intended to cause a smaller than normal grain structure in gold. If not used exactly right, they can cause hard spots and localized discoloration. Iridium (Ir), Nickel, (Ni) Chromium (Cr), and others.  More on this later as we discuss tools and equipment.

 

Why do grain refiners not respond well to the small shop torch caster?

Keeping high melt element in even distribution through an alloy is not easy. Induction machines are best for this sort of alloy, since they often mix the alloy by nature of the frequency used, and usually have superior atmosphere control. That atmosphere control allows the use of far less silicon deox than what most torch casters need. Torch melts may or may not keep iridium, chrome or whatever in true suspension in gold.


Fuel, Oxygen, Metallic Chemistry

 

Lets talk about how atmosphere and gases react to add to our mix of alloys. This is the actual chemistry we deal with,  whether we understand it or not, we face the results. When we discuss air, we really mean oxygen.

 

Reaction of gold with air

Gold metal is stable in air under normal conditions. However gold does dissolve in aqueous cyanide solutions in the presence of air.

 

Reaction of silver with air

Silver metal is stable in clean air under normal conditions

 

Reaction of copper with air

Copper metal is stable in air under normal conditions. At read heat, copper metal and oxygen react to form Cu2O.

4Cu(s) + O2(g)  2Cu2O(s)

 

Reaction of zinc with air

Zinc metal tarnishes in moist air. Zinc metal burns in air to form the white zinc (II) oxide, a material that turns yellow on prolonged heating.

2Zn(s) + O2(g)  2ZnO(s) [white]

 

Why do argon, nitrogen, and forming gases help castings come out clean?

"Free" oxygen is the enemy. Argon and Nitrogen displace air and oxygen. Hydrogen actually harmlessly  consumes oxygen to produce heat. Forming gas is a mix  of nitrogen and hydrogen that gently consumes oxygen.

 

Hydrogen Torch Melt Of 24kt

Torch Fuel Gases

 

Some jewelers use a torch to melt their gold, and some use electricity. Each has its benefits and problems of course. The experienced eye will properly judge the balance of fuel gas and oxygen. A torch when set properly, provides its own protective atmosphere while it provides heat. The person at the torch must also judge when the alloy has reached proper temperature for the next step, whether that be casting or pouring a bar to roll out. Like our alloys, torch heat depends on the reaction of elements, usually in compounds like natural gas. Lets talk about gases that can be used with oxygen to melt precious metals. I'll list them with some notes about each..

 

Natural gas

Sometimes called "city gas," natural gas is a mixture of several hydrocarbon family compounds, primarily methane and ethane. This gas is a bit weak on heat, but there is a natural (forgive the pun) safety advantage-the gas comes from the city pipe as needed, so there is not a tank of explosive gas sitting in the room with you. You are, however, still stuck with that tank of oxygen. In some areas such as the very cold northeast, the content of the gas you receive can vary with the season or the availability to your city source. This is the most commonly used gas in small to medium capacity shops. Natural gas is also the only gas commonly used in blow furnaces, which are found in many large silver casting houses. For large melting jobs, a forced-air blow furnace offers a great reducing atmosphere limiting the formation of oxides.  If you do not have natural gas service and would like to use something 99% the same, ask your welding gas supplier for Methane. For our purposes here it is identical to natural gas except you have that tank of gas sitting in the building with you. Not as safe as piped in gas, but this stuff works well on gold and silver.

 

Acetylene

This gas is the dirtiest gas I see being used in the jewelry industry. Acetylene is what they use at the local muffler shop to weld steel. Acetylene offers lots of heat--and lots of carbon soot as well, making it very hard on your gold. In addition, acetylene can react with copper and silver alloys, making it less than ideal for use in jewelry manufacturing. Acetylene tends to stay in pockets rather than dissipate, and as with all the flammable gases, acetylene can explode if it builds up. It is also shock sensitive, so cylinders must be handled with extreme care. Acetylene is one of the least expensive gases to refill, and the regulators for it are similar to hydrogen regulators in cost.

 

Propane

Propane is a hydrocarbon family compound commonly used in areas where natural gas is not available. This gas burns fairly cleanly but it needs plenty of oxygen to boost the heat. It tends to be a bit hard on the metal, since with higher oxygen use, oxidation becomes a proportionally greater problem. This gas is stored in a small pressurized tank in a liquid state. Regulators are simple and inexpensive, and refills are as close as the nearest gas station that sells propane to the RV and bar-becue crowd. A safety caution: Propane is extremely heavy and explosive, so be sure to ventilate properly. The tank should not be stored indoors at all.

 

Hydrogen

This is by far the cleanest gas you can use. Hydrogen is a simple element, with no bound-up carbon at all. The heat of combustion (the amount of heat that a standard amount of substance releases on combustion) is two to three times higher than that of other fuels. The byproducts of burning hydrogen are heat and water--hence the clean burn, a very practical advantage. Hydrogen is also the only gas recommended for melting platinum alloys.

All the other flammable gases (compounds all not pure elements) provide hydrogen with another attached element, such as carbon. Hydrogen is a high heat gas and very, very explosive. (High heat and explosive potential always come together.) Hydrogen is extremely light, so it rises away from you quickly. The gas molecule is so small it will flow through almost any opening in the ceiling or roof material, which usually allows it to disperse harmlessly. If hydrogen becomes trapped, however, it is extremely hazardous, so adequate ventilation is essential. You'll use far less oxygen to boost the heat with hydrogen than with other gases. Less oxygen is universally a plus when melting precious metals, since fewer oxides will form.

 

The Argument for Hydrogen-The #1 element

I have a hard earned bias toward hydrogen as the best gas for silver gold and platinum, melting or soldering. This comes from witnessing countless torch castings done with all kinds of equipment., and seeing the results. In addition, because we actually refine at PMWest I would melt scrap gold into grain for refining. The grain would look great when compared to the tired blackened tree


Chemical reactions of the gaseous elements and combustion

 

Reaction of hydrogen with air

Hydrogen is a colorless gas, H2, that is lighter than air. Mixtures of hydrogen gas and air do not react unless ignited with a flame or spark, in which case the result is a fire or explosion with a characteristic reddish flame whose only products are water, H2O. 2H2(g) + O2(g)  2H2O(l)

 

No carbon needed to add heat! Hydrogen gets its heat from a uniquely clean simple chemical reaction. No further complications are present. When we discuss the advantages and shortcomings of fuels every other source of heat involves carbon reactions with oxygen, creating as many as 200 less understood chemical reactions to deal with.

 

Reaction of carbon with air

Carbon, as graphite, burns to form gaseous carbon (IV) oxide (carbon dioxide), CO2. Diamond is a form of carbon and also burns in air when heated to 600-800C - an expensive way to make carbon dioxide! That's how jewelers and alloy manufacturers see it. What follows is how chemists see our work. I will include both descriptions where needed so we can clearly discern what really effects us all as users of precious metal alloys.

 

C(s) + O2(g)  CO2(g)

When the air or oxygen supply is restricted, incomplete combustion to carbon monoxide, CO, occurs.

2C(s) + O2(g)  2CO(g)

 

It is important to note that many crucibles are made of graphite, a form of carbon. Unlike diamond, graphite will react with oxygen at fairly low temperatures. When you cast gold or silver in a graphite crucible, it gives up its like, atom by atom reacting with free oxygen to create more heat and more carbon gases. If you want graphite crucibles or dies to last longer, make sure that oxygen is kept away while the graphite is too hot to touch. Smart casters will buy the crucible cooling accessory that accepts a neutral gas feed.

 

*At the simplest level, natural gas burns (oxidizes) to produce water(H2O) and carbon dioxide (CO2). At combustion temperatures, methane (CH4--the principal component of natural gas) is broken into fragments or radicals: CH3, CH2, CH, and C, the carbon atom.  These intermediate species are very reactive and free to react with oxygen (O2) and its fragments (O atoms) or nitrogen (N2) and its fragments (N atoms).  Research has shown that there are over 200 possible reactions for methane combustion alone, even more for the other fuel constituents of natural gas, such as ethane, propane, and butane. *This information drawn from The Gas Research Institute web site in an article written by Thomas L. Cramer

 

Natural gas is CH4, that is to say one part carbon for 4 parts hydrogen. Propane is C3H8 three parts carbon to eight parts hydrogen.  Hydrogen is H2-All hydrogen no other elements.

 

Hydrogen is really the only part we need to melt any precious metal. Oxygen and hydrogen combine with combustion to create clean heat (heat and water are the byproducts ) in excess of 5000 degrees Fahrenheit  That is much more than the temperature needed to melt platinum, let alone gold or silver. Hydrogen/Oxygen balance can be adjusted as needed. A reducing atmosphere is best for gold and silver, an oxidizing flame is best for platinum due to hydrogen/platinum reactions that are best avoided.

 

Some important safety notes about fuel gases for torch casting-

Any gas that contains enough energy to melt gold or platinum has enough energy to cause injury or death. Every gas has risks, even the non reactive ones like argon or nitrogen. Understand your tools, and the gases they run on thoroughly.

 

Heavier than air flammable gases generally are frowned upon by fire safety guidelines. In Los Angeles high rise buildings they are forbidden. If a leak occurs, they can accumulate and find an ignition source. That means the last loud noise the victims ever hear, and a large fire to follow. Acetylene and propane are the most common heavy gases we use in combustion. Argon is a neutral; gas that can displace oxygen as intended in the more advanced casting machines.

 

Natural gas is adequate if you will melt gold or silver.  If you will melt platinum for casting or fabrication, you will need hydrogen or propane. Natural gas can be bought in compressed tanks, as methane. This gas is for our purposes identical to natural gas. One important difference is that natural gas comes in through your meter as it is used. Methane or any other compressed gas sits near you in large quantity. 

 

Cooking With Electricity

If you use electricity to melt your alloys, be sure to be very mindful of atmosphere control. One surprise that has come up of late- Nitrogen sold to us as manufacturers, is 90% nitrogen on a good day. There have been repeated reports of oxidation occurring when nitrogen is used.  Enough air got in the gas mix to damage the hot alloy. Graphite crucibles are damaged by oxygen when hot as well. Ask your gas supplier to give you the most pure gases he can. This problem  is less common with argon, and unheard of in forming gas. The following is an excerpt of an article I wrote for AJM magazine that ran in 1997, and is a good summary of technological issues with electricity.

 

Making Electrons Work for You

Electricity is the energy source for both induction and resistance melters. Both types of machines are relatively safe, clean, and quiet, and like everything else that is technology based, they have been much improved in the last couple of years. Jewelers generally find fewer restrictions on electric melting than on gas melting from both land lords and fire departments. This is at least partly due to the fact that in electric melting, the heat is contained in a very small area. In addition, the idea of having ranks of explosive, high pressure gas in the same room with people worries some landlords and firefighters. (An explosive controversy?!)

 

If your shop shares space with a retail showroom, you also run into stricter f-ire safety rules imposed on public spaces. Any non retail shop in an industrial area will have an easier time using processes, such as torch melting, that can present a safety hazard. Public areas face tougher safety regulation, for very good reason.

 

All electric melters depend on a thermocouple to regulate the heat. The more accurate the thermocouple, the more consistent your results will be. Herein lies the source of many problems. Most of the troubleshooting calls we get at PM. West have to do with temperature control.

 

One easy and fast way to check your thermocouple's performance is to melt some fine silver. This melting temperature is constant at 1,762F so you can calibrate accordingly. Alternatively you can call an electronics technician for a more "professional" (i.e., expensive) adjustment.

Electric melters also generally have a tough time isolating gold from oxygen in the air, which causes oxidation. A neutral "gas cap" like argon is the most common solution to this problem. A more aggressive method is using a reactive cover gas such as hydrogen, perhaps mixed with inert nitrogen. This mix is commonly known as "forming gas."

 

Resistance melting

Resistance melting is best known in the small, lower capacity machines, such as Kerr's Electro-Melt or Memco Electro-Vac casting machines, although some continuous casting machines also use resistance melting. All resistance melters use some kind of high temperature wire (like the wire in light bulbs) wound into a spiral outside the crucible. When electricity moves through, the wire offers resistance to the electricity and becomes hot enough that heat radiates through the crucible to heat the metal. Resistance melters are safe to use and very simple in construction, which makes maintenance easy. They're also relatively inexpensive, especially compared to induction systems, and safe to use. A complete casting machine is usually less than $10,000, and a small dedicated melter runs about $800. Crucibles can be delicate and a bit expensive, ranging from $35 to $60.

 

Induction melting

Induction melting is becoming much more common in our trade. This powerful technology used to be reserved for the large scale caster or melter, but not any longer. As platinum casting, stone in-place casting, and mass merchandising of light goods have become more common, they have encouraged more firms to up-grade to induction melting. The induction method uses radio frequency energy at medium frequencies (6 to 12 kilo-cycles) or high frequencies (300 to 500 kilo-cycles) to "induce" heat directly into a special part around the crucible, the crucible itself, or the metal.

 

Different frequencies have different qualities and produce different results. For example, medium frequencies offer the major advantage of actually stirring the molten metal. The current trend is away from high frequencies, but both types have their adherents. Despite many phone calls to machine makers and visits to shops, I've never found a consensus on which type works best and why. Many shops that have a new induction melter make the mistake of overheating the metal at first. Because the induction method is so powerful and the timing is quirky, many folks "overcook" the melt, just as many of us have done to dinner with a new microwave oven. Keep in mind that timing is very important in induction casing. When the induction coil shuts down, the temperature of the gold falls quickly--much faster than most thermocouples can measure.

 

There is even a new ultra-high-tech type of pressure/vacuum caster that has variable frequencies. This variable setup solves the control problems associated with time delays inherent in thermocouples, as well as the myriad inconsistencies caused by the differences in one melt versus another.

 

Another variable to consider when using induction melting is the differing rate of heating between the crucible and the alloy. This is addressed by data access and artificial intelligence software, such as that found in the Neutec J-5 and the Romanoff / Yasui casting machines. With the advent of scene-in-place casting, many induction-melting casting machines are also showing up with pressure vacuum capabilities. Induction melting requires lots of juice. Often you need to install special high voltage circuits to feed this energy hungry animal. In addition, these melters need a supply of cool water to pump through the "induction coils" (really the antenna for the radio energy) so that they do not overheat.

The cost for induction melting systems can vary widely. The range is from about $5,000 for a dedicated melter without casting attachments to $70,000 for a pressure/vacuum casting system featuring induction melting and artificial intelligence software. In addition, with all this technology maintenance can he a big part of operating costs.

 

A less expensive level of induction melting costs roughly between $15,000 and $30,000. Memco, Inresa, Erschem, and other suppliers offer a wide variety of these machines. These induction melters are usually part of a complete casting machine. They can be bought as separate devices, bur problems with open-air oxidation reduce the advantages of separating melting from the casting machinery. The solution for oxidation problems is a neutral gas cap such as argon or nitrogen, or even a reactive gas like flaming hydrogen.

 

A disadvantage with the "all in one" casting machines is you cannot alter the speed of the pour during the cast, as you can with a torch and hand pour. 'The precise casting equipment setups are too varied in detail to discuss here, but all attempt to melt rapidly to protect your precious metals from oxidation, and they all automate as much as possible to ensure consistency. These machines can isolate you to a greater degree from your processes, which can he a good or bad thing, depending on your management philosophy The advantages of isolation include consistent results during repeated castings of similar type, some additional safety features, and fewer problems when personnel turn over. A perceived advantage is a lower pay scale in the casting room. The disadvantage is that when anything goes wrong or you change the casting process, whether it's changing to a different karat gold or moving to stone-in-place casting, there's no one there to teach the machine and the operator what the differences are. The machine can hardly teach the crew!

 

A common misconception is that if you buy a highly automated machine, the person who runs it does not need to be highly skilled. Some will disagree with me here, but I believe that the more skilled the person, the better the results month in and month out--regardless of the machinery's sophistication. There is no substitute for highly trained and experienced people-with all that implies, including a good salary.

 

Besides casting, the most common use of electricity is to melt metals for a bar or ingot. In this case, the metal is either extruded (continuous casting style) or poured into a steel or graphite mold. When choosing an induction unit, be very specific and tell the salespeople exactly what you will melt, and what kind of crucible you will use. The sales and technical folks can advise you about how much power you need and what frequency range is most suited to your needs. Flask sizes can be important for efficiency and crucible types are varied and have their own material and design criteria. The sales rep can help you sort through all these variables and find the machine that's right for you.

 

If you're considering adding a new process like casting to your shop, be thorough in your research. When you understand the tools available as completely as you understand your shop's needs, you'll make the best choices.

 

 

 

Memco Electro-Vac

 

#34 Alloy draining water after pour

 

 

#100 White Alloy

 

The Alloy Story-The first mix of metals and heat

From these elements, we create all kinds of alloyed gold for manufacturing. We make Yellow, White, Green and Rose. We use gas torches, induction, and electrical resistance to melt. We spin or vacuum to cast. Fabrication, rolling and stamping alloys all draw from the above list of elements. Some of you will note I barely motioned a few rarely found metals out, like grain refiners. They are intended to assure a very small tight grain structure in cast metals. Grain refiners or nucleators work well only in tightly controlled circumstances. This is a point where I must also respect the proprietary concerns of my employer, and others in the gold alloy trade, and our customers. Some of the additives were closely held secrets until a few years ago. My employers' father founded a firm (the Former PMRefining, Buffalo), which pioneered the use of silicon as a gold deoxidiser in the United States. 

 

Balancing Act

It's important to remember that the balance of metals has every kind of effect on the outcome. Karat sets gold content by the relevant percentage. Karat limits the area we can work in for metallurgy. Only 25% of the metal in 18kt! Beyond yellow or white, what tint of  color will work best in your line? Then we need to know how the jewelry will be made. Ideally, we would have any behavior from any color in any karat. Of course, reality comes up short. Just try making 22kt white gold in a soft malleable form.  

 

Casting Alloys 

The vast majority of gold casting alloys contain a silicon deoxidiser to improve the raw cast condition of the tree. Silicon allows many of us to avoid bombing and stripping. When trees break out clean, polishing goes much easier and faster. Another valuable benefit of  silicon aims right at the checkbook. "Recast ability" This may be the most common request in the alloy trade because less gold is purchased for any given production. We call gold that has been cast too much "spent" metal. "Spent " metal must be refined or replaced and either is costly. We always recommend a 50% minimum fresh metal 50% cast tree ratio. The difficult reality is that in a pinch, casters will cast whatever they have. Occasionally gold is cast to death like this. Silicon has a profound effect on the grain structure.

 

Use too much silicon and you will have problems, like cracking or a poor finished surface. Too little and you have metal that is too oxidized for use.  Do consider what kind of casting equipment you have. If you cast with very hot gases like Hydrogen, or natural gas, you have lots of heat available for any kind of gold or silver. Electric resistance melting (seen in small relatively inexpensive electric machines from smelting to casting) can be weak heat wise. This means white gold will be more of a struggle with some resistance equipment, particularly if it a bit old or worn out. Induction is great technology, as seen in the latest machinery, but is relatively costly. When you  choose alloy formulas, you will see a need for more additives in open air melt situations (like a torch, Handy Melt resistance, or open air induction) than in enclosed machines like the Neutec "J" series of induction casting machines. One advocate of his sophisticated enclosed, induction, pressure/vacuum claims you should use no deoxidiser in gold for that machine. Opinions vary on this; my experience shows that the flask has enough oxygen in and around it to affect the gold. The proof? Cast fresh deoxidized gold and then some fresh non-deox gold into different flasks keeping all else the same. The deoxidized gold breaks out cleaner looking than the non deox.  

 

Fabrication Alloys

It really is crucial to match an alloy to the job. Fabrication alloys should not include silicon deoxidisers. As mentioned elsewhere, the grain structure is changed by the silicon. Better for casting but silicon ruins the metal for rolling and fabricating. Some jewelers can roll casting gold on a limited basis, but you are much better off using an alloy designed for rolling when you plan to do so. In the highest karats like 22kt, gold completely dominates the color. Yellow is almost all there is in very high karat. 22kt is very soft by mature, again due to the soft nature of gold itself Fahrenheit Extreme malleability makes this a great fabrication gold, with brilliant rich color. 22kt has too much gold content to cast very well for most of us. Gas porosity is the most common difficulty, with shrink being a big  factor as well. 18kt yellow fabricates beautifully, with a minimum of trouble. Alloys that are about half copper and half silver heat treat quite well, allowing items like money clips to work quite well. I suggest palladium alloys for fabricating 18k white. Expensive while palladium remains high, but the workability is a pleasure.


 

 

Silicon Deox Suggested Use Chart

 

 

 

 

 

Torch

Electric

Resistance

Induction

 (Open air cast)

Induction

 (Enclosed with inert Gas)

10-14 yellow casting

Yes

Yes

Yes

Yes at reduced levels

10-14 white casting

Yes

Yes

Yes

Yes at reduced levels

10-14 green casting

Yes

Yes

Yes

Yes at reduced levels

10-14 rose casting

Yes

Yes

Yes

Yes at reduced levels

18 yellow casting

No

No

No

No

18 white casting

No

No

No

No

18 green casting

No

No

No

No

18 Rose casting

No!

No!

No!

No!

Fabricating of any Karat and Color

No!

No!

No!

No!

 

 

 

       

Rolling Mills for Fabrication

 

Yellow Gold

With 18k yellow, we have the ability to adjust from a dark reddish (higher copper lower silver) yellow up through the standard yellow, and even into the green tints. Remember, additional silver in the alloy makes a more greenish yellow. More copper gets you a darker, redder tint. The majority of the metal being yellow (75% gold) makes it easy to keep a yellow color.  When you are going to cast 18kt, you may have trouble with brittle castings if you use a deoxidized formula. When you use "non-deox" alloy (usually means no silicon additive) the trees will come out of the flask a bit dark. Just use pickling, or tumbling to remove the oxidized surface material. Deox alloys do recast nicely with less fresh metal, but at higher risk of brittle or cracked rejects. High silver alloys are a lighter yellow with a green tint, familiar to fans of Italian 18kt jewelry.

 

In lower karats, we need the alloy to be yellow as well as the gold. Otherwise, we would get very poor color. For example, if we mix gold with pure silver at 14kt, we get pale green soft gold. If we mix 14kt with only copper, we get very red but brittle gold. Therefore, when it comes to yellow, we use alloys that superficially resemble brass. When we go down to 10kt, alloy properties take an even larger role. For casting, you generally do want deox type alloys. The vast majority of alloys for 10kt - 14kt contain (in most likely order, exempting the gold) Copper, Silver and Zinc. There are exceptions; the recently popular "Peach" tone of yellow in 14kt or 10kt can come from alloys that are copper and silver only or with minimal zinc.

 

Make sure your alloy supplier knows how you are going to melt the gold. If you use a natural gas torch, you need an alloy that differs in additives from the proper alloys for induction casting- particularly the newest hyper-technological pressure vacuum systems.  In general, open torch or resistance melt casting requires more deoxidiser than the very sophisticated closed system machines. Additives are great to have but they must be matched to the work and tools at hand. 10kt can and does cast very well, but can and does tarnish with time. Most alloys that work in 14kt will work very well in 10kt, so you do not need to keep separate alloys for each. That is nice when you get an order for 14kt, and can add 24kt to your stock of 10kt instead of buying too much new gold.

14ky Gold

 

Green Gold

Green gold is simply a mix of mostly silver and gold in whatever karat. The green is fairly light, and many tri-color jewelry makers actually electroplate the light green gold parts with a bright green plating of gold. Green gold is very soft, but tends to be difficult to cast well. Too mush precious metals without enough of that ever helpful element copper. Gas porosity and a bad grain structure are common issues.

 

White Golds

The next color to deal with is the much feared "white" gold. Like most alloys, white is primarily copper. The active ingredient for this color is nickel. This common base metal is a very mixed blessing. A very small percentage (thank goodness!!!) Of nickel is needed to achieve white gold. In 18kt (including the 75% gold) the nickel content may be as low as 5% or up to about 7%, and we get reasonably white color. Excluding the gold for a moment, we see from 10% to 33% Nickel content in these alloys.   Rhodium will still be called for to get the whitest possible color in 18k. Like yellow gold, most alloy additives are for casting white. The softest versions for rolling and fabricating contain no additives, just the right balance of base metals, silver and gold. Some white gold alloys contain no silver at all. We almost never see Nickel based white alloys with high silver content. For some, silver and nickel do not react well with one another. Others seem to mix them just fine, probably with very proprietary methods, which may not be consistent. 

 

Some electric machines struggle to melt white gold.

When we use electricity to create heat we use one of two methods. On the lower side of the budget scale- Resistance (The use of a spiral wire which will tolerate large inputs of electrical energy, while producing heat) works well up to about 2000 degrees Fahrenheit.  Above that and the melt may not be consistent. When a resistance machine is old, or at capacity, nickel or palladium gold alloys may not blend properly or cast well. Many small resistance machines lack atmosphere control, which contributes to wear and tear on the gold alloy, silver alloy, and crucible.

 

 

White gold either really white or really soft never both.

With white gold, think in terms of trade off's- The whitest alloys contain the most nickel. However, nickel is the cause of both excessive temperatures and excessive brittleness. The first trade off. workability vs. color. The next trade off-lower nickel mixes that feature lower temperatures tend to have poor color. Another awkward trade off is the problem of the silicon and the nickel forming hard spots that are real trouble. However, if you do not use silicon additives in casting you will need a lot more fresh gold all the time.  Like other alloys, white casting alloys usually contain silicon or boron additives. White alloys are mostly copper, with some nickel, and then small amounts (sometimes none) of silver-excluding the gold, nickel content in white alloy runs from 15% to 30%. Keep in mind that white golds cast at a higher temperature than yellow. This means you will get more reactions with the chemicals in the investment. 

 

In 18kt, we often see palladium based white alloys that do not contain nickel. Palladium is not as good as nickel for color. Palladium makes a very malleable 18k white. They do also typically contain lots of silver, up to 80% excluding the gold of course. If one is going to bead set in 18k white, palladium white is the way to go, despite the expense. Palladium alloys cost from about $125.00 up to $250.00 per ounce (plus the gold!) and nickel alloys run about $1.00 to maybe $6.00 per Toz. A huge difference at least while palladium stays expensive.  European nations have restricted Nickel content and emission in jewelry items.. Sending good jewelers scrambling for an affordable alternative. Time will tell..   In 14kt or 10kt white, the color can be very good; some do not bother using rhodium at all. The trick is to make gold that is malleable enough to set and size easily, yet still be very white. Because we are using so much alloy (as much as 58%+, the majority of the mix in 10kt!) it really makes sense to use exactly the right alloy and no other. I used to see white gold jewelry sold at a higher price than yellow; market forces have made that almost disappear. White gold is more difficult, and therefore more costly than yellow. 

 

Rose Golds

Rose gold in 18kt is very, very difficult to get right. Gold by nature does not stay mixed with high copper alloys in 18kt. As the molten rose gold freezes, the copper separates back out and ruins the item. Copper is the active color ingredient of course, being the sole red metal we use. If we blend the copper with silver we get useful metal but at cost in color intensity. Like white gold, we compromise color for behavior. Casting 18k rose gold is best avoided. If you must cast 18k rose, use a non-deox alloy. The grain structure needs all the help it can get.  After you cast, quench timing will make or break your castings. Too soon, or even a bit too late and you get a mess.  

 

In 14kt or 10kt we can get excellent rose color in lighter or darker tones. The lighter tones contain more silver and are much softer than the darker mixes. Again, use deox alloys for casting, and non-deox for fabricating. Good rose gold solders are available; unfortunately, the best rose color still comes from cadmium type solders. Other solders do not have the same color, or flow at a high temperature.  

Rose Gold Tree in Copper

 

Sterling Silvers

Most commonly, silver is alloyed with pure copper, to make classic sterling silver. 92.5% Silver, and 2.5% copper is official formula. The copper causes hours of work when the sterling tarnishes. Remember all the polishing our moms or grandmothers did on the family silver?  Technically, silver tarnish is usually sulphur and silver oxide, or a more contaminated silver oxide compound, but I'm told by chemists that silver oxide is not black at all like copper oxide. One would expect that tarnish removed from traditional sterling would actually be copper oxide, but that is not strictly the case. Apparently the copper somehow triggers an accelerated darkening of the surface, even though the darkened material may mot be any form of copper itself. There seems to be a difference between jewelers observed results and the actual chemistry, and that is a mystery I'll continue to research. In recent years, various alloy makers have substituted other metals in sterling for the copper to get rid of or reduce the oxidation or tarnishing.  These alloys are all different from one another, and use all kinds of odd elements like germanium or tin to accomplish this interesting feat. Non-tarnishing silvers are usually softer than classic copper/silver sterling. All are 92.5% silver or a bit more, and all require exact  processing to avoid porosity.


 

Exotic Colors Of Gold

 

Purple

Purple gold is made by blending aluminum and gold.  This alloy is very difficult to make. Aluminum is extremely light, gold is heavy. Aluminum has a very particular way about atmosphere, we use helium to weld aluminum to aluminum, let alone mix with gold. That fact alone shows that some elements will not happily blend with gold. Anyone who manages to successfully blend these two elements deserves a round of applause and a patent. I say this because after you blend these elements, even with other ingredients to assist, the resulting alloy will be brutal to use as jewelry. After casting, you might as well think of the blue gold as opal. It is just as brittle. Imagine trying to set a stone in a stone. If you drop your piece of purple gold on a hard surface, it will break.

 

I have seen one famous designer work on purple. He had a very custom, sophisticated set of equipment. He was also very practiced in working at the "Bleeding edge" of precious metallurgy. His purple was very brittle, and very bright in color. Experience shows that the color verses behavior trade-off  is common in Precious metallurgy. You cannot go to school for this stuff!

 

Blue

Mix iron with gold to get this color. Most of the above applies, very brittle. No setting, no engraving, no pushing of metal at all, just like turquoise. Most often found used in some sort of inlay method. Very rarely used. It's just too difficult to produce in large quantity.

 

Black

Every example of a true black color I have seen in person, is a patina or surface treatment. The "black" shown below is really a dark blue, which will patina black.

 

Brown

Sometimes made with lead of all things. Too bad it's so toxic to produce or wear. Again, a very brittle nature goes with the exotic color.

 

Either the metals will not happily mix like copper and silver and gold, or the atmosphere is all wrong.

 

In my opinion, until we can step beyond neutral or reducing atmospheres for casting and up to exotic gas atmosphere casting, annealing, soldering and polishing, and perhaps even setting these colors will remain beyond most of us. I look forward to someone proving this opinion wrong. Step on up!

 

Color

Karat

Gold %

Silver %

Copper %

Zinc %

Palladium%

Tin %

Iron %

Nickel

Cadmium*

Beryllium*

Aluminum

Thorium*

Bright Purple

20

83.3

 

 

 

 

 

 

 

 

 

16.7

 

Blue

18

75

 

 

 

 

 

25

 

 

 

 

 

Grey

18

75

 

8

 

 

 

17

 

 

 

 

 

Black

14

58.3

 

 

 

 

 

41.7

 

 

 

 

 

Brown

18

75

6.25

 

 

18.75

 

 

 

 

 

 

 

Purple

18

75

 

 

 

 

.5

 

 

 

 

 

1.5

 

The above chart shows some historical formulas. They are not recommended, and some metals are very toxic or dangerous like cadmium and thorium. However, this should satisfy your curiosity on exotic gold colors.

 

 

Bottom Line.

No matter what kind of jewelry you make, there is a variety of modern alloys that fit your needs. Just gather the information you will share between your production people and your metal suppliers. Karat, color, and manufacturing processes are all key facts. Maximize the information flow and you will enjoy the benefits of the right alloy in the right job. 

 

Credits & Gratitude

Web Elements- Pictures of Atoms/Reactions of Elements With Air/Thermal reactions

Keith Weinstein , CEO Keith Weinstein Inc.

AJM magazine in cooperation with MJSA

Marc Robinson, former COO Precious Metals West/Fine Gold

The Gas Research Institute web site in an article written by Thomas L. Cramer

Ganoksin.com and the Orchid Discussion Forum

Suzanne Wade-The kind former editor of AJM who convinced me to begin writing for the trade-Thanks Suzanne!

 

 

24kt Gold Sponge

 

Alloy For Rose Gold

 

24kt Gold Grain
 Reference Charts

Karat

Gold  %

Alloy %

10kt

41.66

58.34

14kt

58.33

41.67

18kt

75.0

25.0

Useful Percentages

 

Karat Raising Factors

 

 

Karat Wanted

10k

14k

18k

Karat On Hand

 

 

 

0k

0.714820

1.399998

3.000000

10k

 

0.400000

1.333336

14k

 

 

0.666667

 

To raise the karat of your gold-Find the raising factor at intersection of karat wanted and karat on hand. Multiply the weight of your karat gold by the raising factor. This will give you the weight of 24kt you need to add to reach the correct karat.

Karat Reducing Factors

 

 

Karat Wanted

10kt

14kt

18kt

24kt

1.400000

0.714384

0.333330

18kt

0.800000

0.285715

 

14kt

0.400000

 

 

 

To reduce karat: Find reducing factor at intersection of Karat on Hand & Karat Wanted. Multiply the weight of your karat gold on hand by the reducing factor. This gives you the weight of alloy you must add to reach the correct lower karat.

A crucible for each gold prevents contamination
Conversion Chart For Common Units

 

Unit

Conversion

Chart

Convert from:

Convert To:

Multiply By

Carats

Dwt.'s

0.1286

Carats

Grams

0.2

Dwt.'s

Carats

7.776

Dwt.'s

Grams

1.5552

Dwt.'s

Ounces, troy

0.05

Grams

Carats

5

Grams

Dwt.'s

0.64301

Inches

Millimeters

25.4

Kilograms

Ounces, troy

32.1507

Kilograms

Dwt.'s

643.014

Millimeters

Inches

0.03937

Ounces Avoir.

Ounces Troy

0.91146

Ounces Avoir.

Grams

20.3495

 

 

 

 


 

Properties of Natural Gas and Propane

Properties of

Natural Gas

Propane

Chemical formula

  

CH4

C3H8

Boiling point of liquid at atmospheric pressure

F

-258.7

-44

Specific Gravity of vapor (Air = 1)

  

0.6

1.53

Specific Gravity of liquid (Water = 1)

  

0.6

0.51

Calorific value @ 60 F

BTU/cu ft

1012

2516

BTU/gal

  

91,690

BTU/lb

  

21,591

Latent heat of vaporization

BTU/gal

712

785

Liquid weight

lbs/gal

2.5

4.24

Vapor volume from 1 gallon of liquid at 60 F

cu ft

  

36.39

Vapor volume from 1 lb. of liquid at 60 F

cu ft

  

8.547

 

 

 

 

Amount of air required to burn 1 cu ft. of gas

cuft

9.53

23.86

Ignition temperature in air

F

1200

920 - 1020

Maximum flame temperature in air

F

3568

3595

Octane Number

  

100

Over 100

 

Using  Precious Metals West alloys

Precious Metals West - Fine Gold alloys often contain a special deox additive which, when used correctly, allows the castings to breakout of the investment bright and shiny. Just light pickling is required to remove investment. No stripping or bombing is necessary.

 

Metal   

You must use at least a 50% new to old rejuvenation for our alloys to perform as stated above. We cannot guarantee our metal's properties if this formula is not followed. Any metal will discolor if proper amounts of new metal are not added keep this in mind..... Metal temps should be slightly higher with the deox alloys. If temperature control is not available, inspect your crucible after each cast to insure all metal leaves the crucible, with no beads or flashing of gold remaining. Never cast straight from alloying-- alloying temps are considerably higher than casting temp. Allow metal to cool first, or pour karated gold into water first. Then proceed with casting.

 

Dowse

We suggest you wait until all color leaves the button in dim light. This varies with flask temp, from 8 to 15 full minutes. If running full production, cast 5 - dowse 1. (NOTE: Always dowse flasks completely underwater, and wear an appropriate dust filter mask to avoid silica powder poisoning).

 

 

 

Melting

If torch melting, use cleanest and hottest gas available. We highly recommend Hydrogen/Oxygen with 40-60 lb. settings, utilizing a medium-sized rosebud torch. Natural gas fluctuates in pressure and lines are consistently dirty.  Propane is very weak heat-wise but acceptable. Acetylene is totally unacceptable due to large amounts of soot, and safety issues with a heavier than air fuel. Most areas that allow public access may not use propane or acetylene due to the explosion and fire risk. Electric metal often allows air to get to the hot gold, which can cause severe oxidation and porosity. Ideally, use a hydrogen/nitrogen "forming" gas to actively consume any oxygen before it can affect the copper in your gold. If you can not use a forming gas, then be sure to use argon or nitrogen gas as a barrier to prevent air from affecting the gold alloy. Air ruins hot gold! Crucibles for white  gold should never be used with yellow gold & vice versa. For those of you who use "city gas". Sometimes a gas company will change the content of their supply. (Usually on cold winter days). Try to use hydrogen & oxygen for best results with all precious metals.

 

We operate many kinds of casting and production equipment. If you have a vexing casting problem, call us and let's talk through the problem. If needed, you can send us waxes and casting to evaluate for problems and cast ourselves to find the solution you need. Our alloy customers enjoy this service at no charge. Who else can offer this level of support?

 

Apparent Casting Problem

Likely Solution

Small holes (porosity) oxidation in holes, spots on surface

Incomplete burnout or very high casting temperatures

Poor fill in or internal holes.

Flask temperature too cold.

Porosity in large rings with no oxidation.

Flask temperature too hot cool down 50 to 100 degrees F.

Rough castings.

Investment not mixed properly, or too old.

Bubbles on rings.

Poor vacuum, check vacuum table and pump.

Cracking usually at sprue.

Shrinkage caused by improper spruing or quenched too quickly.

Metal sticking to crucible, sluggish pour.

Metal is not hot enough.

White gold  has hard spots.

Gold was not properly blended with white alloy.

Reddish brown  color as raw castings, black spots.

Insufficient fresh gold.

 

 


Oven Controller Chart

 

This is a scan of our actual chart from our oven controller. It provides a record of each cycle.

 

Note that the first three hours or so are at or below 200 F. to avoid cracking from water becoming

steam in the body of the plaster.

 

Then about 100 degrees per hour up to 1300 F.  Four or five hours at 1300, then descend over

three hours to your casting temperature.  The total time is about twelve hours.

 

  2007 Keith Weinstein Inc.

 

 

 

 

Daniel@preciousmetalswest.com