I just noticed that the link doesn't work so I will post what it says. Blue Bowl micro Gold recovery system
Hand panning concentrates smaller than 20 mesh is difficult and tedious, even an expert panner loses a lot of micro fine Gold. The Blue Bowl, used properly will recover Gold as fine as talcum powder.
Equipment needed: Blue Bowl, gem tumbler, gold pans, 20, 50, and 100 mesh sieves, 20 gallon plastic tub, 4 gallon plastic buckets, sniffer bottle, tumbler, cast iron skillet, vinegar, table salt and wetting agent.
Classify your material into different sizes, Gold larger than 20 mesh can be picked the out with tweezers, and can be processed using a micro sluice or Gold wheel, i.e., Desert Fox, Gold Genie, etc. Gold smaller than 20 mesh calls for the Blue Bowl. After processing your concentrates with a Blue Bowl, place prescreened minus 20 mesh concentrates into a tumbler, add acidic acid "white vinegar," and tumble over night. Remove the concentrates from the tumbler, then rerun them in small quantities in the Blue Bowl, using a small scoop. When finished, extract the Gold with your snuffer bottle.
Mix the remaining black sand, and the black sands discharged from the Blue Bowl with equal amounts of table salt. Place the mixture into a cast iron skillet and heat until mixture is scorching hot and completely dry. Pour the hot concentrates into a plastic bucket or small tub of cold water. This procedure fractures the attached Gold from the sodium and black sand. Collect the processed concentrates and rerun them again using the Blue Bowl at a reduced water pressure and water level.
This process will take extra time, but you will recover the micro Gold conventional panning washes away. After the concentrates have been processed, remove the Gold from the Blue Bowl using a snuffer bottle. Is it worth the extra effort? You bet! More often than not, there is 4-7 times more micro Gold than visible Gold in your black sands. I threw away a small fortune in micro Gold in my haste to clean up the concentrates of an eight inch dredge. A mate turned me on to using a Blue Bowl to reprocess my black sands during the winter months after dredge season closed. At the end of the season I might have twenty, five gallon buckets of black sand. From a single bucket I recovered 25 dwt before tumbling and roasting using the Blue Bowl. The black sands had been screened and processed using a popular Gold wheel before I tried using the Blue Bowl