Contrast: Use a Spectrophotometer to determine the opacity of paints and coatings

Understanding the Opacity Formula

Opacity is measured directly by the contrast formula. A visual representation of this formula would be a paint, coating or paper sample of color measured against a pure black and pure white sample background and quantified according to the CIE Y (lightness or lightness) value system. The percentage calculated by this formula will give the contrast as a numerical percentage of the product's opacity.

Contrast and opacity play an important role in a variety of industrial applications, including paint films and powder coatings. Also known as "hiding power", the contrast measurement has been standardized by ASTM (American Society for Testing and Materials) as a "parameter for production control and purchasing specifications. The greater the hiding power, the less coating per unit area is required to obtain adequate hiding power. Therefore, knowledge of hiding power is very important to paint cost and compare paint values."

Measuring Contrast with a Spectrophotometer

Both contrast and film thickness play an important role in determining the hiding power and opacity of paints and coatings. Several methods can be used to calculate these specific variables, including visual and instrumental assessments. The ASTM Visual Evaluation Test Method is a practical and inexpensive method for determining the hiding power of paints and evaluating coating by "brushouts", but human perception is highly subjective and does not always provide a clear picture of the contrast score . Therefore, ASTM developed Test Method D2805 which uses a Spectrophotometer for evaluation to accurately quantify contrast and help create uniformity and consistency in sample measurements. Determining percent contrast ratio using a Spectrophotometer provides objective color measurement readings that are ideal for the automotive industry as well as industrial applications for various building materials where color matching and quality control are desired.