The fineness of a gold alloy is expressed in 'carats'. Pure gold is '24 carat gold'. Gold is used in dentistry because of its softness and resistance to corrosion. Demand in this area is declining, with its substitution by cheaper non-gold alloys and ceramics. The electronics and space industries use gold's properties of electrical conductivity and heat reflection.
Gold has applications in radar equipment, home computers, satellites and the space shuttles.
Gold film has been used in the glass windows of modern buildings to reflect heat. Gold salts are used for toning in photography, and in colouring glass. The gold contained in hard rock has to be extracted by chemical leaching after the ore has been crushed and finely ground. After grinding, the ore is leached in large agitator tanks,nearly always with cyanide in solution. The material in the tanks at this stage is known as 'pulp'.