Definition - What does Fish Eyes mean?
Fish eyes are a type of coating defect which is characterized by circular voids or separation in the coating. Fish eyes are small, crater-like openings in the finish after it has been applied. They are usually caused by oil and grease on a coating substrate.
In car painting, the term "fish eye" refers to a tiny crater that can form on a car's paint job during or after the car is repainted.
Fish eyes are also known as silicone contamination, poor wetting, saucering, pits, craters and cissing.
Corrosionpedia explains Fish Eyes
Fish eyes are a typical defect when paint is sprayed. They are small quasi-circular areas of substrate that are exposed through the applied coating immediately after application and which have at their center a source of contamination. Fish eyes can be caused by oily spots or silicone particles and/or by airborne droplets that are deposited on the painted surface.
When a coating is applied to a substrate that is contaminated with low surface energy particles such as oil, wax, grease or silicone, fish eyes may develop in the coating as it is applied. These fish eyes are produced because the coating is unable to wet out the contaminated area.
Potential causes of fish eyes include:
- Improper or insufficient surface cleaning or preparation
- Effects of old finish or previous repair
- Contamination of air supply
- Oil, wax, grease or silicone contamination
- Use of silicone-containing polishes or aerosol sprays in proximity to the spray area
Reduction of surface tension is required to avoid fish eyes. This can be achieved by surface-modifying agents such as surfactants. Apply light coats of base coat until defect is covered. In severe cases, sand the affected areas, clean thoroughly, isolate and refinish.
In automotive applications, as an example, several substances can cause fish eyes, but the main way to avoid these craters from forming on a car's finish is to clean the car thoroughly before painting it. Protect the car during the painting process, and ensure that nothing gets onto the paint.