Many find it odd, and it’s starting to seem odd to me, too: for thirty years, namely for the entire middle part of my active life, I was occupied with the production of paints—that is, liquid substances that, spread in a thin layer, after a certain time become solid, spontaneously or when heated. I find it equally odd that, on my “lower level,” memories of paint are replacing those of Auschwitz. I notice it in my dreams, from which the Lager has disappeared by now, but in which more and more frequently I am confronted by a paint-related problem that I can’t solve.
Of course, I just gave a somewhat simplified definition of paint. Beer and seawater, too, if they evaporate as a thin layer, leave a solid residue, but nevertheless they can’t be called paints. In other words, paint has various other general and special characteristics that are known to all, and so there is no point in making an effort to define them here.
In the course of my career, I was confronted with many strange problems. For instance, I was asked once for a paint that could be applied to the insulators of high-tension power lines and that would change color in a way that was clear, irreversible, and visible from the ground whenever an insulator overheated, even just for a few minutes. Many years earlier a more frivolous problem was presented to me. A dandy who was purporting to be a cosmetics manufacturer asked me to study a colored paint, “for evening,” to be applied to the teeth the way you apply nail polish. At the end of the evening, it should be removable with a non-toxic solvent—in practice, ethyl alcohol. I was to come up with the product, and he would take care of a high-profile commercial launch.
I don’t think I devoted more than fifteen minutes to this question. I tested a green concoction that was presumably suited for the purpose on my own teeth; the outcome was so disgusting that I immediately called the dandy to tell him I was not available for his project. Another time, I was asked for a glossy black paint that would dry quickly and cost very little. It needn’t be weatherproof, insisted the customer—who was a coffin manufacturer.
Apart from these oddities, phenomena where liquids become solids continue to have a special appeal for me; you can’t expect a soldier to forget the battlefield. A paint factory is also a factory of stalactites, and this, too, is a passage from liquid to solid. But while natural stalactites take millennia to grow, ours take only weeks. Often the tanks are not watertight. Drops of paint that leak from them solidify before they fall, and turn into graceful short candles with a hornlike consistency that are mercilessly uprooted and thrown in the trash. They can be stocky or slender, transparent or colored; at times they are forked or in clusters. They grow slowly and silently like upside-down mushrooms.
The passage from liquid to solid is never a dull spectacle, as anyone knows who has witnessed a pig-iron casting cool or a flow of molten lava burn itself out. “Cooked” wax that solidifies in a cauldron takes, spontaneously, the elegant shape of a crater, while colophony, which retains some fluidity until it solidifies, sets in a glossy and smooth mirror, “Narcissus’ mirror.” And what about freezing water? Often a dirty city puddle, after a winter night, turns into a delicate mesh of jagged crystals tens of centimeters long; and the fact that no two snow crystals are exactly alike is proverbial.
We are at the edge of a forest of symbolic meanings, so that solidification is felt in turn as positive or negative, as reassuring or deadly. Blood coagulates, in most cases beneficially, at other times (inside its vessels) causing a fatal thrombus. It’s always a dramatic phenomenon, though, and fabulously complicated. And everyone has heard of rigor mortis.
The most wondrous solidification I’ve ever come across, however, is a completely different one. It’s the solidification of spider’s thread. Spiders are resourceful little creatures toward which—as I have already related—I have strongly ambivalent feelings. None of the patterns one normally encounters are applicable to the instantaneous solidification of a spider’s thread. Could it be simple freezing—just as water, cast iron, and wax solidify when they are cooled below a given temperature? Surely not: a spider always has the temperature of its environment and its tank can’t be warmer than the air. The spider’s spinneret, seen under the microscope, is very similar to the one through which nylon is extruded, but this analogy is illusory: before passing through the spinneret, nylon is molten, at over 250°C.
Could it be that a solvent evaporates, just as it does with paint? No: no solvent has ever been found in the tiny body of the spider, except water, which evaporates slowly, while the solidification of the spider’s thread is instantaneous; it turns from liquid to solid as soon as it comes out of the spinneret—otherwise the spider wouldn’t be able to hang from it. Moreover, if it were evaporation of a water solution, the thread should be soluble in water, which is not the case; even when just woven, the spiderweb withstands rain and dew very well.
Could polymerization occur: could, in other words, long, and therefore solid, molecules, develop from a “soup” of smaller molecules contained in the spider’s glands? Chemists don’t know any polymerization process that occurs in a fraction of a second, and, so to speak, “on command”—that is, following the mere passage from a closed environment to the open air. They do know processes whereby solids are formed by mixing two liquids, but the spider possesses only one raw material.
The solution to the problem has been known for a few years, and its simplicity is disarming. The liquid secreted by the spider’s glands, and stored above the spinnerets, becomes solid when subjected to traction. It is made of molecules long enough to be solid, but they are rolled up into a ball and therefore slide on one another: in other words, they are a liquid, although very viscous. But the spider secretes the thread always and only under traction: it “pulls out” its thread. Now, the nature of this liquid is so delicate and peculiar that a modest stretching is enough to cause an irreversible solidification: the knotted molecules stretch out and become parallel threads. All caterpillars that make cocoons use the same mechanism; this is how silk originates.
No chemist has yet succeeded in reproducing such an elegant, simple, and clean process. We have overtaken and violated nature in many fields, yet from nature we still have much to learn.
La Stampa, November 9, 1986