Fabrication with 24K
PureGold

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
during setting.

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 the metal.

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 upon
heating.

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 a
piece.

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.