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.
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
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
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.
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.
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
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.
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.
Most
of the following ingredients are used by alloy makers to make your work
easier to accomplish.
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.
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.
Used
in certain proprietary/patent alloys to increase hardness after heat treating.
Very effective when used correctly.
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.
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.
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.
