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Precious Metallurgy Issues
the implications of alloy
behavior and jewelry manufacturing practices.
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.
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.
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
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
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.
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.
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
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.
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
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.
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
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
materials were produced and we began shipping two formulations in 2001.
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.
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.
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.
color is very good, comparable to most nickel based alloys and superior
to some. Rhodium is appropriate to prevent time tarnishing and to improve
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.
"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
of the following ingredients are used by alloy makers to make your work
easier to accomplish.
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.
reputed deoxidiser, this really helps offset the poor effects of silicon.
Nearly always found in alloys containing silicon to offset the above mentioned
in certain proprietary/patent alloys to increase hardness after heat treating.
Very effective when used correctly.
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.
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.
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
metal is stable in air under normal conditions. However gold does dissolve
in aqueous cyanide solutions in the presence of air.
metal is stable in clean air under normal conditions
metal is stable in air under normal conditions. At read heat, copper metal
and oxygen react to form Cu2O.
+ O2(g) 2Cu2O(s)
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.
+ O2(g) 2ZnO(s) [white]
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.
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..
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.
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 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.
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
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
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)
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.
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 600-800°C
- 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.
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.
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
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
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.
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.
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.,
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 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.
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
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
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.
Alloy draining water after pour
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
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.
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
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.
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.
Mills for Fabrication
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.
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.
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.
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.
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.
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, 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.
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
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.
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.
Gold Tree in Copper
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.
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.
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!
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.
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
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.
the metals will not happily mix like copper and silver and gold, or the
atmosphere is all wrong.
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!
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.
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.
Elements- Pictures of Atoms/Reactions of Elements With Air/Thermal reactions
Weinstein , CEO Keith Weinstein Inc.
magazine in cooperation with MJSA
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
Suzanne Wade-The kind former
editor of AJM who convinced me to begin writing for the trade-Thanks Suzanne!
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.
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
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.
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.
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).
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?
is a scan of our actual chart from our oven controller. It provides a record
of each cycle.
that the first three hours or so are at or below 200 F. to avoid cracking
from water becoming
in the body of the plaster.
about 100 degrees per hour up to 1300 F. Four
or five hours at 1300, then descend over
hours to your casting temperature. The
total time is about twelve hours.