Machines used to grind aggregates into very fine particles or to apply very high shearing forces within a fluid to produce colloid suspensions or emulsions in which the particle sizes are less than 1 micrometer. One type of colloid mill is called a disc mill, in which a mixture of a solid and liquid (or two liquids) is passed between two discs a small distance apart, which rotate very rapidly relative to each other. Other types of colloid mills are the valve and orifice types, in which the mixture is forced through an orifice at a very high speed and then strikes a breaker ring. Applications of colloid mills occur in food processing, in paint manufacture, and in the pharmaceutical industry.