Small Batch Refining Processes for Natural Gold Projects

James Hutchings

— 3 min read

I provide small batch smelting for custom processing of the gold miners natural gold.

Gold as it comes from the stream or concentrated free milling gold from hard rock contains oxidized forms of Silver, Copper, Iron, and some Rare Earth minerals. Along with remnant Quartz, these need to be removed from the gold to make it nearer to pure gold. Using a small tornado furnace, soda ash, and borax glass, the gold is heated to melt to consolidate the silica quartz up and into a glass cap. The glass cap also absorbs the oxides of the other metals, contaminates, and prevents oxidation of the remaining gold, silver, and copper.

The remaining gold is considered "Dore", the first smelting of gold. From time to time, the process is done twice if the first smelting is not complete or the glass cap is heavily contaminated with the byproducts. There are some losses in the volume of gold from raw to Dore, as much as 1 to 2 grams per one half ounce. the smaller the gold flake and fines, the more the losses.

The Dore is roughly 23 1/2 Karat gold and is ready for casting or the addition of alloys for durability in jewelry use.

The Dore is melted along with a commercial alloy of Copper and Silver, and often a little Zinc or other proprietary minerals. The 14 karat gold end product requires 42% alloy to the 58% near pure gold. As you can see, the addition of alloy nearly doubles the volume of casting gold for use in your custom cast product. 10 karat extends the volume of raw gold even further. Gold at 18 Karat and Dore are considered too soft for most jewelry products, but can be cast if desired.

The finished product cannot be marked 14 karat as it is not likely "plumb" or within tolerances established for marked and marketed precious metals by law. We need to understand here that the Dore still contains a very small amount of natural iron. The iron causes crystallization in the final cast product and can cause the gold to be somewhat brittle. This brittleness is not usually a problem in cast products, but does not allow us to roll the gold into sheet products nor pull wire stock from it. We can hammer it as the ancient artisans did, but it does often crack and require soldering or heating and hammering to bring the metal back together. In gold rings, brittleness can limit the extent to which the ring can be sized up and down. It is preferred to remove metal from a thick shank to size up, or adding a strip of gold sheet stock to size down where possible. A jeweler should be made aware of the natural gold product when submitting the piece for repair or modifications. To this date, we have not experienced a ring failure due to brittleness, but it is an issue that should be kept in mind. Recast of fractured rings is offered at 1/2 of the original casting price if required.

Once the gold is alloyed, conventional lost wax processes are used to cast an object. A wax model is selected from a catalog or a custom wax is carved to specifications. The wax is set in a high temperature flask, imbedded in an investment batter, cured, then heated in a kiln to melt out the wax. The remaining cavity, brought up to temperature, (roughly 900 degrees F) is placed in a centrifugal caster and the melted metal forced into the flask and mold.

The casting is cut from the sprue channel, filed and cleaned, and then polished.

Simple gold bands and rings average less than $200 to process from raw gold to finger ready. There is a reduced cost for second and third rings from the same batch in the same casting flask. Prongs and stones or gold nuggets can be added to the final product at an additional charge.

Custom Lapidary

I provide custom lapidary services on most all stone materials.

  • Finished Cabochons
  • Polished slabs
  • Bookends
  • Large stone and petrified wood carving and polishing
  • Gem carving
  • Re-polish of existing opals, turquoise, other semi-precious stones in and out of settings
  • Re-lamination of opal doublets or triplets
  • Replacement and Restoration of intarsia or missing melee stones.
  • Beach stones, crystals, abalone, and sea glass are polished as is or cut and polished and set in Sterling as jewelry.
  • Elks teeth, bone, and other odd materials are cut and polished and set for jewelry use.

Lapidary service is at the rate of $40.00 per hour, most single stones are done on a material type and specification basis. Multiple stones are discounted. Generally, a cabochon can be completed from slabbed material at around $15 to $20.

Silversmithing and Goldsmithing

I provide custom silversmithing and goldsmithing of conventional and custom projects. Setting cabochons in a simple sterling silver bezel generally runs $30 to $40. Otherwise, I am glad to entertain custom projects from pictures or drawings and provide quotes. I am glad to take clean scrap gold in exchange for gold sheet stock for projects to keep the project cost down when requiring gold settings. I can also work in Gold Filled material for cost savings.

Traditional jewelry repair, sizing, and retipping are also offered.

Restoration of pieces that are not generally accepted by most jewelers are considered a challenge and reasonable quotes are made. Keep in mind that many older pieces may be restored for casual wear only and not for day to day use.