Stradivari Varnish oil/resin ratio in The Pegbox Posted August 29 · Report reply 7 hours ago, sospiri said: If the oil or varnish goes black as we see in some old instruments and paintings is this because it is oxidizing without polymerizing? Are you sure this is not dirt building up? There is no good reason why a black colour (massive absorption) should develop - at least I can't see this at the moment. In some of these Southgerman instruments the black colour is caused by the use of dichromate which is a massive oxidant. Theer the surface of the wood turns black. For which makers have you seen this blackening?