At Cauer Violins, we do all the cleaning outside in a well-ventilated area. As soon as we get a little whiff of the chemical, we move a few steps further to avoid exposing ourselves to the fumes. To avoid contact with the liquid, we take a sheet of Kleenex, make a wad out of the larger part of it and hold it so that the wad extends outside of our fingers. We put some Xylene on to the lower surface of the bunched up Kleenex and hold it at the dry upper end.
Even though we know that xylene will not harm the vast majority of varnishes, we always carefully try it out on a little area towards the edge. If a clean area becomes sticky, or when the tissue shows color other than the green grey color of violin dirt-rosin-polish, it is advisable to discontinue.
Notable exceptions on which xylene should never be applied are most of the modern Cremonese violins from 1980 to today and the violins of the Carl Becker & Son family. The fact that xylene dissolves certain varnishes does not reflect on the quality of the varnish, as the beautiful Carl Becker violins aptly demonstrate.
When cleaning a violin while strings and bridge stay in place, we take all precautions that the bridge does not get moved from its place. To facilitate cleaning under fingerboard and tailpiece, we wrap a tissue around a flexible 6-inch ruler and move it carefully up and down under these areas. A coffee stick may work too. When all the dirt is gone, the instrument may show a little semi milky film over the varnish, which gets removed with a soft micro-fiber cloth (or cloth made of very soft cotton). When buffing it this way, one should avoid pressing in the area of the f flaps. The arching of the top does not support this area, and you can create a small f flap crack from the lower round hole up to the C bout. The cloth used for buffing should not be too large. If too much of the cloth floats around behind the hand like a comet tail, it may get caught in the f hole, at the tuner, or at the bridge and damage parts of the instrument. A violin maker does not buff but polishes the instrument with a liquid, which is a solvent of varnish. The finish is a bit nicer, but it acts as a varnish remover in the wrong hands and should never be attempted by anyone who is not a professional restorer.