- On close examination, a fish eye is a perfectly round pock mark in the finish that is rimmed around the outer edge like a moon crater. Inside, there appears a small white dot. When viewed overall, the mark bears a striking resemblance to a fish's eye. Other marks often coined by the same term will lack the rim or the dot, and instead may be caused by a surface that is too porous.
- These fish-eye blemishes occur when the surface tension of the stain is not compatible with the surface tension of the floor. A variance in these two tensions is usually caused by the presence of silicon or some type of oil. Things such as diesel fuel or fumes cause fish eyes. The same is true of substances containing silicon, which vary from furniture polish to hairspray or from the atmosphere to hand lotion or soap introduced by the person finishing the floor.
- Work in a protected environment, if possible. Clean the wood with mineral spirits or naphtha and heavy scrubbing to remove any traces of silicon or other oils. In some cases, a layer of wax-free shellac may also inhibit the formation of fish eyes, although this is not recommended for areas where flammability is an issue. Wear a Tyvek-type suit and hair net, and use only silicon-free toiletries such as soap, shampoo, hairspray and lotion before applying finish to the floor.
- To further aid the avoidance of fish eyes, use a fish-eye eliminator, which is a silicon-based additive that's mixed into your finish. The additive balances the surface tensions between the finish and the surface, allowing it to flow smoothly and evenly. Be careful to thoroughly clean your tools after using an additive; otherwise minute traces of the eliminator will have the opposite effect and cause the formation of fish eyes in your next project, unless you use the additive again.
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