The weirdest part of the gold refining business may be the bags filled with old teeth. "This is the worst thing we handle, by far," said Brian Wallis, general manager of Dillon Gage in northwest Dallas. Most of what passes through the refinery isn't as creepy: boxes filled with old rings and bracelets, stacks of bent forks and silver serving trays, sacks with busted electrical parts that contain bits of silver and gold.
The Dillon Gage refinery - and others like it - are the answer to this question: What happens to my scrap jewelry when I sell it?
The rings and forks and candelabras and teeth are separated into precious metals and less precious materials. They're melted and assayed, dissolved and purified, then sold to mints and jewelry makers and other markets.
The refinery is especially busy these days because more people are selling their jewelry and metal heirlooms to companies that aggregate the material and send it along.
Other sources include dental supply houses that send teeth with old fillings and bridgework with high-quality gold and silver. The refinery also accepts air filters and polishing dust from jewelers, even old carpets from jewelry factories. Embedded in the dirt, cloth and trash are minute amounts of gold that are worth the cost of processing.
The refinery is in an unremarkable building in an industrial neighborhood. There's no sign on the door - on purpose. Security is important, and the business does not want walk-up customers, though a few arrive at the front door.
"When somebody finds us, they're lucky," said company president Terence Hanlon.
Most of what is refined at Dillon Gage is sold to mints to make pure gold and silver coins.
While the company has the latest in environmental technology, the basic process used to measure and refine precious metals would be familiar to an alchemist from 1,000 years ago. The metal is melted to help determine its value, then purified using powerful acids.
Here's the process:
Each lot is separated into piles of gold or silver, then weighed and tagged. Jewelry with stones worth salvaging is set aside for a separate process.
Gold goes into one furnace, in a graphite-clay cup that can tolerate a temperature of 2,200 degrees. Silver goes into a slightly cooler furnace
In the winter, the furnace room is pleasantly warm. In the summer, it can hit 147 degrees.
The gold and silver are assayed, or measured, to determine how much is precious metal. For instance, 14-karat gold is about 48 percent pure gold; the rest is less valuable, usually copper, zinc or nickel.
Each lot is melted down and a sample is taken and weighed. Then the sample is remelted in a cup about the size of a shot glass made of powdered lamb's bone. The cup absorbs everything that's not precious metal. Once the metal hardens, it is reweighed. The difference between the first and second weighing identifies exactly how much precious metal is in the original lot - and what it's worth.
After the assay, the company makes a purchase offer to the seller: more than 95 percent of the value of the pure material on the open market, minus a processing fee.
Getting the assay exactly right is important because gold is so heavy and so valuable. A kilo (1,000 grams) of pure gold is smaller than an iPhone and worth about $30,000.
The metal is then dissolved in a bottle filled with powerful acids.
Jewelry with valuable stones goes straight to this step. The acid doesn't harm the stones while it dissolves the metal. Dental scraps, rugs and air filters are burned first to get rid of most of the nonmetal and pulverized before getting the acid treatment.
Gold is so resistant to chemicals that it requires two acids to dissolve it. But eventually the gold, along with the other metals it had been mixed with, vanishes into the acid like salt dissolving into water.
After the metal is totally dissolved (a process that takes a couple of days), one of the acids is chemically neutralized. The gold then settles to the bottom of the bottle as a pure powder that is dried and melted into small blocks.
A similar process is used to filter out pure silver.
The other less valuable metals are later dried out of the remaining acid and sold.