In the past, most dry concentration was slow and inefficient. Even today, some dry washers have trouble recovering gold after the top layer of dry sand has been removed, due to the moist sand and gravel below the surface. New technological improvements allow modern units such as the 151 drywasher model made by Keene to help dry out this material and increase gold recovery to very high levels. Don't miss our drywashing books and videos - CLICK HERE