At the end of a day on the "diggin's" you've got ounces or pounds of pan or sluice concentrates. Now you carefully pan out the yellow metal you've worked so hard to get. But no matter how careful you are, there are obvious impurities in your pay-off. Any more panning would get rid of the impurities, but also a lot of gold, too. Cleaning your gold into a marketable condition while saving all possible gold is something you should learn to do, and there is not a better teacher on the subject than Allen Mershon.
Allen, as the club program chair, he has arranged many fine presentations for us. At the September club meeting, he himself was the show.
A good first step in gold cleaning is to dry and size-classify the gold. For drying, heat the gold in a stainless steel pan. But do this only in a well-ventilated area! There may be toxic material present which can vaporize and become extremely dangerous! If you don't have a lot to clean and you're not in a hurry, you can use a gold pan or cookie sheet and dry it outdoors or use a blow dryer indoors.
After the material is dry, the next step is to classify (screen) the gold. The number of size-fractions to use depends on the size range of your gold. Locally, two sizes are enough Call one "coarse" and the other "fine." The divide between the two is 40 mesh. Note that "fine" refers to particle size, NOT purity. But as a matter of fact, the finer the gold, the purer it will be. That is because as the gold in a running stream breaks down into ever smaller particles, more of the contained impurities are exposed to the environment and oxidize or otherwise disappear. Locally, the gold in Clear Creek has an average purity of 960 (parts per thousand), Platte River gold 920, and Buena Vista (Arkansas River) 800. As you might expect, you can find some nuggets at Buena Vista, but you will not find anything larger than 1/8th inch in Clear Creek.
Commercial screens are good but expensive. A cheaper alternative are hobby-store screens. Window screens are around 17 mesh. When the gold has been size classified, you can more easily remove the impurities. A sniffer bottle, used dry, is useful. You can also put the gold on a sheet of paper or glass and gently blow off the impurities. Or copy the dope dealers from the TV cop shows and use a glass plate and a razor blade. Your last move is to use a magnet. Always "hover" the magnet above the sample. Always clean gold over a smooth surface or container to catch spills.
To estimate the purity of gold, check the color against gold jewelry of known purity. Gold dealers typically discount by 25%. Your yield will be something like: daily spot price -20% X 31.1 X the gram weight of your gold. (31.1 is the approximate grams per troy oz.) There may be a bonus for -20 mesh gold. Buy or borrow a scale to check weights before you deal. Or have a standard weight to checkthe dealer's scale. Refiners want a minimum of 10 ounces of gold (Au). Or you can simply hoard your gold for the day when the world economy collapses, and you will be royalty! But in any case clean your gold so that your friends won't look at it and say "Hey, what's that stuff in your gold!"