The carat is a unit of purity for gold alloys (24-carat gold = 100 % pure gold ). Tissot uses 18-carat gold ( 75 % pure gold ) in the manufacturing of its watch cases and bracelets. Depending on the required colour, the alloy changes slightly :
- 18K yellow gold is generally made of 75 %
gold, 12.5 % silver and 12.5 % copper ;
- 18K rose gold is obtained by adding more
copper than silver ;
- 18K white gold is obtained by adding more silver
( or palladium ) than copper.