Opacity

The terms "contrast ratio", "opacity" and "hiding power" are used interchangeably throughout the coatings industry. Opacity is defined as the ability of a coating to prevent the transmission of light. A practical example of this is the case where a yellow wall is painted using a red paint. The greater the opacity the red paint, the more efficient it will be at hiding the underlying yellow colour

Opacity is defined by how a wet film of the test coating is applied to a black and white patterned substrate. After the film has dried, a reflectance meter or a spectrophotometer is used to measure the amount of light reflected from the overcoated black areas of the substrate. This is then expressed as a percentage of the amount of light reflected from the overcoated white areas. This value is the opacity of the film.