.800 Purity Mark Incorporated in a Swiss Maker's Mark. Silver Watch Case, First Quarter of the 20th Century.
.800 silver is an alloy of silver that is 800 parts silver and 200 parts other metals. It is also referred to as International Coin Silver. This alloy was common in the 19th and early 20th centuries on the European mainland but was not used in jewelry in the United States. 800 silver was the alloy of choice for pieces decorated with niello because it can withstand high firing temperatures better than alloys with a higher silver content.