3 New Acid Test Needles. This is a new set of 3 acid testing needles. These needles test 10K, 14K and 18K gold. They are used to determine karat content of gold. The needles and the item to be tested are rubbed on a test stone and treated with acid to determine a match. We work hard to update our descriptions and pictures of our merchandise. As part of a process of ongoing innovation by our suppliers, newer versions of the item shown may be shipped before we are able to complete an update. As a result there may be a slight variation in color and design.