Seeing a gloss meter may not be something on your bucket list. But as a wood coatings guy, I spend a lot of time dealing with gloss. When I saw this BYK Gardner gloss reading device (at IWF 2012) I was surprised to find it was about the size of a 6-inch sub sandwich.
Gloss (also called “sheen”) is measured by shining a light on the coating at a specific angle, then reading the intensity of the reflection of the light. The more that’s reflected, the glossier the coating. In clear coatings, where reflections can come from within the coating itself, the unit of measure for the reflection is given in terms of the percent of light that returns to the gloss meter.
click image to zoom There are no strict woodworking industry standards, but there are general ranges: A dull sheen is usually around 15% reflection; satin around 35%; semi-gloss about 65%; and gloss is 80% and higher. Within opaque coatings it is not unusual to see different sheen names, e.g., eggshell, flat, wet look. (The latex paint on my walls is satin eggshell sheen.)
So how do we manipulate gloss or sheen in a coating? Paste and powder modifiers are available, but have finite limits. Going beyond them causes problems. To minimize additives, start with a coating closest to the target sheen. It’s best not to start with gloss if you want to go to satin or a duller sheen. If clarity is an issue, spray initial coat(s) with a gloss product; then use the final coat to create the sheen level that you want. The top layer acts as a lens to bring us to the desired sheen.