Perhaps the most widely used piece of equipment for dry gold recovery, is a dry washer. The dry washer is basically a short, waterless sluice. It separates gold from sand by pulsations of air through a porous medium. Screened gravel passes down an inclined riffle box with cross riffles. The bottom of the box consists of canvas or some other fabric. Beneath the riffle box is a bellows, which blows air in short, strong puffs through the canvas. This gives a combined shaking and classifying action to the dry washer material. The gold gravitates down to the canvas and is held by the riffles, while the waste passes over the riffles and out of the machine.
A basic dry washer is composed of a frame in which a well braced, heavy screen is covered with burlap overlain with window or fly screen and covered with fine linen. Above this, riffles made of one-half to three-quarter-inch, half-round molding or metal screen are placed 4 to 6 inches apart. The slope of the box varies from 4 to 6 inches per foot. A power washer of this type can process up to 21 cubic feet approximately 0.8 cubic yards) of screened material an hour. Hand-powered washers operated by two men can process 1 or more cubic yards per 8 hours, depending on the size of the material handled.
If you’re planning to prospect for gold in the desert, than a dry washer is a piece of gold prospecting equipment that you must have. It really has only been in the last 40 to 50 years that you could buy pre-made dry washers quite easily. Prior to that, generally most dry washers were designed and built by the individual gold prospector himself.