24 karat gold has been considered too soft
to manufacture jewelry that will withstand everyday wear. However,
PureGold’s microalloyed 24K gold has greatly improved hardness
and strength when properly carried through the manufacturing process.
This enables the production of jewelry that can carry a 24K hallmark
in almost all countries of the world and yet retains its finish
and structure in everyday wear.
Fabricating a piece of jewelry from PureGold begins with
planning the piece from start to finish. The ability of the microalloyed
gold to increase in hardness with cold work allows one to design
the hardness of each part of the piece being made. The increase
in hardness with cold work and intermediate age hardening steps
is shown in the graph.
For the maximum hardness to be reached, plan a reduction
in wire diameter or sheet thickness of 90%. A decrease in cross
sectional area in whatever shaped piece of metal you are working
generates a cold worked hardness and, if you desire less than the
maximum hardness, you can generate whatever hardness you want as
illustrated in the figure below.
The need for work hardening should be anticipated in the
design stages of making a piece. The amount of cold work required
will vary by the type of item being made. A pin back, for example,
will require significant cold work to achieve maximum strength.
A bezel, on the other hand, should be tailored to the hardness of
the stone that is being set. A fragile stone, such as an opal or
a tanzanite, requires a fully annealed bezel that is worked as little
as possible to retain maximum softness, so the stone is not damaged
In contrast to most gold alloys, PureGold does not require
annealing when cold working the metal. It does not become brittle
even with a 99% reduction in cross sectional area. However, should
you desire to soften the metal, heating at 600 degrees Celsius (1112
degrees Fahrenheit) for 20 minutes followed by quenching will anneal
Assembling components can be the most critical step in
completing a fabricated piece since this step requires applying
some heat to the cold-worked components. As shown in the figure
below, a cold-worked , age hardened piece loses some of its hardness
We produce a 22K solder that will join the metal at 425
degrees Celsius (797 degrees Fahrenheit). This low melting solder
does not significantly decrease the cold worked hardness of the
pieces to be joined and, can be carried out at the beginning of
the age hardening process.
The hallmarking laws in the U.S. allow an article to be
stamped 24K if the gold content is at least 0.997 gold and there
are no solder joints. For a fabricated piece with solder joints,
the law requires a purity of 0.993 gold for a 24K stamp to be applied.
Therefore, when designing a piece to be made from PureGold, keep
the number of solder joints to a minimum. The following illustrates
how one can calculate the amount of solder allowed in manufacturing
- Multiply the weight of the piece by 0.007 to figure
out the amount of non-gold elements that the piece can contain
and still meet the hallmarking requirements. For example, if the
piece weighs 10 grams, it can contain up to 0.07 gram (10 x 0.007)
of non-gold elements.
- Since you are working with a microalloy, there are already
non-gold elements in the alloy. For example, the PureGold microalloy
already contains 0.0015 non-gold elements. If you have a 10 gram
piece made of PureGold, it already contains 0.015 g (10 x 0.0015)
non-gold elements. Therefore, the amount of non-gold elements
you can add from the solder is 0.055 (0.07-0.015).
- Since 22 karat gold solder contains 2/24 parts of non-gold
elements or 0.083 gram non-gold elements per gram, divide 0.055
by 0.083. That product, 0.66 gram (0.42 dwt), is the amount of
22 karat solder you can use in the 10 gram piece. This is sufficient
to allow several joints in a fabricated piece and still allow
the 24K mark on the final assembly.
Once a piece has been fabricated, it must be age hardened
in order to obtain the maximum level of hardness and durability.
Age hardening requires heating the piece to 250 degrees Celsius
(482 degrees Fahrenheit), holding it at this temperature for three
hours, and then air cooling. When using an oven for the soldering
operation, the age hardening step can be carried out immediately
after soldering by dropping the temperature and following the same
procedure. Age hardening does not result in oxidation or discoloration.
Finishing a piece made from 24 karat microalloy differs
somewhat from finishing a 14 karat piece. If you treat it like a
14 karat piece, you won’t get a smooth surface; the process
is the same, but the number of steps is greater. In fact, polishing
24 karat microalloys is similar to polishing platinum.
A fine finish is obtained by proceeding through progressively
finer abrasives – 200 grit, 400 grit, 600 grit, 800 grit and
1200 grit – before a final rough polish. When applying the
rough polish, use a light touch. Applying too much pressure generates
heat and does little to polish the metal. In fact, it allows the
surface of the metal to soften somewhat and does very little polishing.
Like platinum, microalloys respond well to cross buffing. If you
desire a matte finish, the graded papers available in 2,000 grit,
4,000 grit, 6,000 grit and 8,000 grit allow you to add varying degrees
of fineness to the finished product.