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TIP: Understanding Gloss and Satin

agent coats dries film finish finishing flatting flexner gloss reflecting satin shrink-wraps the finishing store woodfinishing woodworking

It’s the last coat you apply that establishes the sheen of your finish. In other words, if the sheen you’re getting is not to your liking, just apply another coat of finish on top with the sheen you want, and that’s what you’ll get.

Sheens range from high gloss to dead flat. Gloss reflects an image almost like a mirror. Flat disrupts the image so much that you may not be able to see it at all.

All finishes except gloss contain flatting agent that is responsible for the flatter look. This flatting agent (tiny particles of silica, which you can picture as sand though it isn’t) settles to the bottom of the can and has to be stirred into suspension before the finish is applied. The more flatting agent included in the finish, the flatter the effect.

The flatting agent works by reflecting light randomly from the surface. As the finish dries it shrink-wraps the tiny particles at the surface creating a microscopic roughness that screws up the image. The flatting agent in the thickness of the film has no flatting effect because it doesn’t disturb light from passing through. (If you know a little chemistry, the technical explanation is that the flatting agent and the finish film have almost the same refractive index.)

On the example shown I applied two coats of gloss finish to the left half of the panel and two coats of satin to the right half. Then I applied a coat of satin finish to the right half of the gloss side and a coat of gloss finish to the left half of the satin side. The two glosses are indistinguishable and the two satins are indistinguishable even though they have the opposite sheens underneath.

It works this way with all types of finish.



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