Varnish is an unstable substance by definition: in fact, at a certain point in its career it must turn from a liquid into a solid. But this must occur at the right time and place. If it doesn’t, the effects can be unpleasant or dramatic: it can happen that a varnish hardens (we say brutally “monkeys”) during its sojourn in the warehouse, and in that case the merchandise must be thrown out; or that the base resin hardens during the synthesis, in a ten- or twenty-ton reactor, which amounts to a tragedy; or even that the varnish does not harden at all, even after application, and then one becomes a laughingstock, since varnish that doesn’t dry is like a gun that doesn’t shoot or a bull that can’t impregnate. In many cases the oxygen in the air plays a part in the hardening process. Among the various exploits, vital or destructive, which oxygen can perform, we varnish makers are interested above all in its capacity to react with certain small molecules such as those of certain oils, and of creating links between them, transforming them into a compact and therefore solid network. That is how, for example, linseed oil dries in the open air.
— PRIMO LEVI, The Periodic Table