Glossary

R

Reducer
Commonly known as thinner.

Reflectance
The ratio of the intensity of reflected light to that of incidental light.

Relative Humidity
The ratio, expressed as a percent, of the quality of water vapor actually present in the air to the greatest amount possible at a given temperature.

Resin
A group of organic materials, either natural or synthetic, which can be molded or dissolved.

Rheology
The science characterizing fluid deformation or flow.

Roller
A cylinder covered with lamb's wool, felt, foamed plastics or other materials used for applying paint.

Runs
Sagging and curtaining of a coating or paint film, usually caused by improper thinning, excessive film build or poor application techniques.

Rust
The corrosion of steel or iron is an electrochemical phenomena wherein the base metal reverses to a lower, more stable energy state. If the corrosive environment is water or brine, then the corrosion product formed is commonly know as rust.

In the case of other chemicals, such as alkali's or acids, other combinations of iron salts are formed as part of the corrosion product. The electrochemical corrosion process may be retarded or stopped by the proper use of protective coatings.

One preventive method provides an insulation barrier between the corrosive environment and the metallic substrate. This type of protection is exemplified by the painting of structural steel with organic coatings such as epoxies, alkyds and acrylics. An even more effective method is to use a more reactive metal such as zinc. A conductive zinc-filled coating protects the metal by galvanic protection. The zinc sacrifices itself and corrodes in preference to the steel.