Originally Posted by charles Tauber
I've written about his numerous times over the years and won't get into a long-winded repeat here.
The short answer is that the level of "gloss" is a function of how irregular is a surface. Smoother surfaces reflect light in a "spectral" way appearing more shiny. More irregular surfaces scatter light making the surface appear duller, less shiny. The difference between the two is how free of irregularities a surface is. Surface irregularities can be caused by a number of things including, dirt on a surface, scratches, "texture" of an applied finish, pores in wood and particles suspended in an applied finish.
Dirt can be removed with solvents or fine abrasives. One popular solvent that works well on dirt and grease is naphtha (lighter fluid). Dirt can also be removed using a "polish" - most polishes are a combination of waxes and fine abrasives. The fine abrasives removes dirt while the wax leaves a film that fills small irregularities, smoothing the surface somewhat, making the surface appear more shiny.
Abrasives, be they in polishing compounds, or on a backing, such as "sandpaper", come in a very wide range of abrasives from very, very fine to very course. Courser abrasive sheets are often used to level a finish during stages of initial finishing. Doing so removes highs and lows in the surface, evening out the surface - removing ripples, texture left by the finish applicator (spray gun, brush strokes...). While the abrasive levels the finish, it also leaves scratches that impart a dull shine to the finish. Scratches left by abrasives are removed by using a series of progressively finer abrasives with each finer abrasive removing the scratches of the previous abrasive. This is done until a desired level of sheen is reached.
At any point in the process, one can stop to accept the current level of sheen. For example, if one stops sanding with, say, 1000 grit "sandpaper", one will have a dull satin finish. If one continues through successive grits to, say, 12000, one will achieve a mirror finish. (Rubbing compounds are often used instead of or in conjunction with abrasive "papers" or sheets.)
Thus, if an area of a finish is too shiny - due to, for example, repeated rubbing against a shirt sleeve - one can increase the surface irregularities to make that area less shiny, matching a surrounding satin finish. One need only use the right level of abrasive to match the irregularities of the glossy area to that of the satin area. That might well be 1000 grit sandpaper. The amount of actual sanding needed is very small, often not more than a few strokes over the surface.
If an area becomes dull, and cleaning the surface with naphtha or a fine polish doesn't restore the finish to the surrounding level of gloss, one need only polish the area with one or more progressive grits of abrasive sheet or rubbing compound matching the level of surface imperfection to the surrounding level of gloss. This will typically take a bit more rubbing to remove surface imperfections than it takes to add them, in the case of dulling a too shiny surface. For example, for an area that has become dull, one might start with a typical red rubbing compound, rubbing a small amount on the surface with a paper towel. One then progresses to a grey or white rubbing compound, again rubbing a small amount on the surface with a paper towel. That can be followed by one or more final compounds, such as swirl remover or "polish".
Fine abrasive sheets, such as sold by Micromesh, and a few rubbing compounds are relatively inexpensive and will last for a very long time.
Note that some finishes can deteriorate over time and/or due to chemical attack. Those are special cases different than what is described above.
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