This kit is used to verify the gold content in items. This product set is intended for use with gold only. The acid solution changes color based on gold purity. Easy to use: apply a drop of the solution to a small sample of the item on the testing stone. The set includes a high-purity graphite testing stone and acid testing solution. Material: High-purity graphite stone and acid testing solution Graphite stone size: Approx. 4.1 × 1.1 × 7.2 cm Acid testing solution bottle size: Approx. 3 × 1.2 × 4.7 cm Total weight: 90 g Type: Jewelry testing tool Package includes: 1 × Graphite testing stone 1 × 3 mL bottle of acid testing solution Instructions for use: Rub the item gently on the graphite stone to leave a visible streak. Apply a drop of the acid solution onto the streak. Genuine gold will remain unchanged; lower-karat or non-gold metals may discolor or dissolve. If the streak disappears, the item’s gold purity is below the tested karat level.