If you work with lots of gold and need to test the metal, check out this testing stone from RH Preyda.  These stones are made of 100% natural Surgical Black Arkansas Stone.  To use, rub the test needle and test article on the stone, then apply the appropriate test solutions to determine the karat value.  This is perfect for anyone needing to test the karat value of their gold pieces.  Check it out today at Stuller.com/tools.