Fish Eye - Identifying Fish Eyes in Powder Coating

Effective Date: Nov 16, 2018

The term "fish eye" is used to describe a specific abnormality in the coating surface. Fish eyes are soft edged dimples in the finish. They are often confused with starring or the starburst effect due to their circular shape, but they are different abnormalities with different causes.

Fish eyes are often caused by a spot of wax, grease, or other oily substances that were not cleaned from the substrate surface.

Q&A

What causes tiny small pinhole craters? Been having a problem with them. Second coat does fine.

- GEER PERFORMANCE COATINGS on Apr 26, 2020

Without seeing and example it would be difficult to say with any certainty but here are a few potential causes and things you may want to check.1. Substrate contaminant: surface rust or other dry contaminants can prevent powder resins from freely flowing into a uniform finish.2. Out gassing: Some substrate types such as cast alloys or iron, harbor gas pockets trapped in the substrate from the casting process. When heated, these gasses can be released and can cause small holes or blisters to form in the coating. It's a good idea to pre-bake metals before coating them, especially cast metals.

- No Name on Apr 30, 2020

So if the fish eyes are slight and you don't strip the powder and start over, instead pre-bake them to 450 to try and out gas the steel wheel, then coat it for a 2nd time hot do you think they will flow out and cover?

- TURNER DESIGN WORKS on Jun 13, 2019

It depends on if the impurity that was causing the fisheye has completely released. If not, then they could return. If so, then the powder may look fine however, the integrity of the coating underneath, which had the fisheyes before, may be questionable.

- No Name on Jun 17, 2019

You speak about starburst, but you don't talk about the causes, and how to avoid it.

- HOOSIERBOY RESTORATIONS on Apr 8, 2019

That is because this article is not meant to cover "starring". We cover that topic in another article which you can find here... https://www.prismaticpowders.com/learn/50/starring-starburst-what-is-it-in-powder-coating

- No Name on May 7, 2019