The sheen of a finish is measured as the reflectivity of the dried film – that is, the sharpness of an image reflected in the surface. Sheens vary from high gloss to very flat. The contrast between gloss and satin sheens is shown in the accompanying picture.
Finishes are supplied in various sheens, determined by how much flatting agent, which is usually silica, is added. These are usually identified with names such as gloss, semi-gloss, satin, matte, eggshell and flat. The names reflect the manufacturer’s interpretation and are often chosen for marketing purposes, so the actual sheens you get can vary noticeably among brands.
A more exact, and better, method of identification uses a numbering system from gloss (90 sheen) to flat (10 sheen). Some manufacturers, especially those targeting the professional market, use this system.
You can create your own customized sheen by mixing two sheens of a given finish type together, or by letting the flatting agent in one container settle, then pour off the top half into another container and mix the two parts.
To see what you have, you have to apply at least two coats. After sanding the first coat smooth, apply the second and let it dry. This will give you the accurate sheen.
The final sheen is established by the sheen of the last coat applied, not by an accumulation of sheens of all coats. So you can change the sheen on any surface simply by applying another coat with the desired sheen.
Sheen can also be achieved by rubbing the last coat with abrasives. The last abrasive used will establish the sheen, so you could go from satin to gloss, then back to satin and back to gloss. Once you begin rubbing with abrasives, the flatting-agent-created sheen of the finish you’re rubbing is no longer a factor. Satin can be rubbed to gloss, and gloss can be rubbed to satin.
The downside of a rubbed sheen is that it shows scratches more easily than a sheen created with flatting agents. Any light abrasion running across the ridges of the rubbed scratches flattens them and appears as a shallow scratch.