Features: This kit is used to verify the gold content in items! This product set is only suitable for gold. Acid changes color based on purity. Very easy to use. Just apply a drop of this solution to a small sample of the item to be tested The product set consists of high purity graphite stone and acid test water Specification: Material: High purity Graphite Stone & Acid Testing Water Graphite Stone Size: Approx. 4.1 * 1.1 * 7.2cm / 1.61 * 0.43 * 2.83inch Acid Testing Water Size: Approx. 3 * 1.2 * 4.7cm / 1.18 * 0.47 * 1.85inch Total Weight: 90g Type: Jewelry Tools & Equipments Package List: 1 * Graphite Stone 3ml * Acid Testing Water Note: How to use: If you want test your gold ring is real or not, just need rub black stone, and leave a small sample on stone Apply a drop of this solution to a small sample of the item to be tested onto the test stone. Then the real gold will stay on the touchstone, false one will be dissolved or oxidized to blue If the sample disappears, then the item is below the karat of the solution.