A VARNISH is an unstable substance by definition: at a certain point in its career, it must change from a liquid to a solid. This must happen at the right time and place. If it does not, the results can be unpleasant or even disastrous. It can happen that a varnish will solidify (we say, harshly, it “monkeys”) during its shelf-life in the warehouse, in which case the product has to be junked, or the resin can solidify during its synthesis in a ten-or twenty-ton reactor, which can verge on the tragic. Or instead, the varnish may not harden at all, even after application, which is farcical, because a varnish that doesn’t “dry” is like a gun that doesn’t shoot or a bull that doesn’t impregnate.
In most cases, the oxygen in the air takes part in the process of solidification. Among the various vital or destructive processes that oxygen can bring to completion, we varnish-makers care especially about its capacity to react with certain small molecules, such as certain oils, and to create bridges among them, transforming them into a compact and therefore solid network. That is how linseed oil “dries” in the air, for example.
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