Highly
Trained Alloys
By
Daniel Ballard
In
jewelry manufacturing, we depend on highly trained and skilled workers.
Sales, marketing, through accounting and.arguably more than anywhere else
in the shop. Some of the most profitable changes come right from production.
You have learned the right man in the right job makes you money. Just like
the right tool for the right job. This time we discuss the last big piece
of the puzzle-The very elements we use to make "Highly Trained Alloys".
What alloy will you choose for your next production run? Here is what you
need to know to decide.
Lets
start with an alphabetical list of all the elements, mostly metals (technical
properties of which can be found in any periodic table) that we commonly
use for gold and silver alloys. The alloys are made with base metals, all
of which should be the purest available, just like gold. The basic process
is to melt the elements together, mix, and pour through a special atmosphere
into water. The alloy grain is dried, weighed, inspected, and finally shipped
out. Alloy users then combine the alloy with gold to make exactly what is
needed.
Boron-B
This
element is an additive intended to make base metals and some additives
work together with less trouble. If not used properly, hard spots and streaks
can appear in finished product. In most cases, this is not a crucial ingredient;
countless thousands of items of jewelry are made every year without it.
Carbon-C
Carbon
reacts violently with oxygen in combustion, providing heat for melting.
In one solid form, as graphite, we use it in many crucibles. In another
solid form, it is diamond. Truly astounding properties from just one element!
Copper-Cu
The
most common metal mixed with gold by far, copper is used in yellow, red,
white, and (in very small amounts) even in green gold. Copper is very red
in color, and is the sole red metal we can use. Look for lots of copper in
most alloys, and rose gold alloys run 90% or more copper (excluding the gold
of course). Copper is good at bringing up the hardness in all the precious
metals. Traditional Sterling Silver is made 92.5% Silver and the rest is
just copper. Therefore, when you need red or darker tones think copper. Some
countries even use it in platinum.
Gold-Au
Our
favorite element, well understood by most of us. Yellow in color of course,
so we need to get creative to make red, white, or green gold. A very soft
metal indeed, with legendary properties.
Nickel-Ni
Nickel
is what we most often (by far) use to make white gold. This metal does
a better job at whitening than anything else we can use, including palladium.
This very hard metal hardens almost any alloy that includes it.
Oxygen-O
This
corrosive gas provides the extra heat when mixed with a fuel gas like hydrogen
or propane. The root cause of oxidation, we take all kinds of steps to
avoid oxygen's severe effects like porosity and tarnishing.
Palladium-Pd
A
platinum group metal, the only credible substitute for nickel on the market
at this time, and used almost exclusively in white gold applications where
one needs to avoid nickel or have very soft gold to work with. 18kt palladium
white gold is often seen in plates that are bead set or other applications
using an engraving process to set stones. Palladium does not whiten as
well as nickel.
Silicon-Si
This
one is probably the best thing to happen to casting gold since silver.
Trace amounts of silicon are primarily used to reduce the worst effects
of oxygen on hot molten gold alloys-Oxidation and creation of "Cupric Oxide".
These oxides can and do cause porosity that is difficult or impossible
to remove. Silicon is most helpful in 14kt or lower casting golds but
is problematic in rolling or fabricating gold. In 18kt, its use can cause
brittle castings. **See Picture**
Silver-Ag
The second most common metal to alloy with gold, Silver pushes color toward
the green side. Silver is the active ingredient in Green golds of every
karat. It also softens the alloy, and adds many helpful attributes to the
crystal grain structure in most alloys. Silver is found in Silver, Gold,
and Platinum repair solders.
Zinc-Zn
Because
we do make gold jewelry that is less than half gold like 10kt, the alloy
must have a yellow color if we want yellow jewelry. When Zinc is alloyed
with copper, it makes a bright yellow almost gold like color, and is a
very common metal. We call that alloy Brass. Way back when, casters would
buy brass, then add silver to make yellow gold alloys.
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 left 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% 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 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. 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.
Yellows
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.
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.
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.
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?
In
recent years, various alloy makers have substituted other metals in sterling
for the copper to get rid of 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 sterling. All of them are 92.5%
silver or a bit more, and all require exact processing to avoid porosity.
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.
About
the writer-
Daniel
Ballard is National Sales Manager at Precious Metals West, one of the largest
alloy makers. Daniel travels to shops and factories all over the U.S. in
the course of servicing the alloy customers.
5/25/00 9:59:09 AM
Silicon
Deox Suggested Use Chart
|
|
|
|
|
|
Torch
|
Electric
Resistance
|
Induction
(open cast)
|
Induction
(Enclosed with inert Gas)
|
10-14yellow
casting
|
yes
|
yes
|
Yes
|
Yes
at reduced levels
|
10-14white
casting
|
yes
|
yes
|
Yes
|
Yes
at reduced levels
|
10-14green
casting
|
yes
|
yes
|
Yes
|
Yes
at reduced levels
|
10-14rose
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!
|
