Product Short Description: Spot turns a creamy colour it is high quality silver, usually sterling. If it turns black it is coin quality silver and if it turns green it has high amounts of copper and therefore is poor quality silver and a gold colour means a lot of brass, Product Description: Silver testing solution manufacturer and supplier. Place a drop of acid on the object to be tested. 90 to 100% silver, the acid will show a creamy color. 77-90% silver, the acid turns a gray color. 65-75% silver, then the acid will show a light green color. 90 to 100% silver, the acid will show a creamy color. 77-90% silver, the acid turns a gray color. 65-75% silver, then the acid will show a light green color.