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.