One of the old stains used on Maple is nitric acid, it carbonizes the sugar in the wood and brings out the grain. It was, and is, used on rifle stocks, no reason it wasn’t used on violins.
Hey, don’t I know you? The Nitric acid/iron stain has to be heated to turn color. As far as I know, violins were not treated this way. Generally, color comes from colored varnish. The wood would be treated with any number of different substances to seal it. One of which is “water glass”. There were other things used as well, often in several layers. Once the grain was filled and the surface smooth, a colored varnish would be applied to the surface. To the best I have been able to ascertain, this was the general method used...I can easily be wrong.
Stophel
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