Reducing Bench Sweeps Into Gold
Last month, jewelers learned how to increase their return of gold from polishing sweeps in this column. Here is a procedure for bench sweeps
The procedure explained below will remove all organic material (rouge, shellac, rubber, etc.), plus iron filings from your bench sweeps. It also will deoxidize them. The increase in gold return for bench sweeps processed this way is 25%-33%.
To begin, add lye to water until its so saturated that no more lye will dissolve. (Lye is corrosive, so wear gloves and eye protection.) Add your bench sweeps to a beaker or similar container. Cornings Visionware is best (call (888) 246-2737 for a distributor if you cant find it in a kitchenware or department store). Regardless, dont use a metal container!
For every 100ml of bench sweeps add 500ml of the lye-water mixture. Heat this to simmering and simmer for 30-60 minutes. Cool the water to room temperature and pour off the water, making sure not to pour off any particles. Add one liter of water and stir. Let the sweeps settle and pour off the water.
Repeat this rinsing procedure and then dry and melt. If you have a significant iron or steel content, pickle your sweeps (at boiling temperature) before drying and melting.
To melt with a torch, wrap the bench sweeps in tissue paper, soak this in alcohol and use a Bruno-style crucible. If using electric melting, wrapping and soaking is not necessary.
By Peter Shor
Peter Shor is the son of Nathan Shor and is a member of I. Shor Co., Shor International Corp., Mount Vernon, NY; (914) 667-1100.