The Forger's Spell - Edward Dolnick [79]
alligator skin;
dried riverbed
Craquelure arises because an oil painting is a complicated, multilayered object. We sometimes call a painting a picture, but the picture itself—the depiction of a milkmaid working or a woman reading—is only part of a complex structure. In a typical seventeenth-century oil painting, the artist began with an untreated canvas (or, less often, a wooden panel). Then came a succession of layers, each with a distinct role. First, the canvas was sealed with a thin coating of glue made from rabbit skin, to protect its fibers from the slightly acidic layers soon to come. Next came the so-called gesso layer, this one of glue and chalk, meant to fill the gaps in the canvas’s weave and produce a smooth surface. There followed an oil-priming layer, made up of chalk and linseed oil. The aim here was to smooth the surface even further, the better to be painted on, and also to seal off the gesso layer. If a careless painter skipped the oil priming, the absorbent gesso would suck the oil out of the paint and produce a leathery, wrinkled surface.
At last, after all this preparation, came the picture itself. It, too, consisted of layers, because paints differed in just how opaque or translucent they were. In Vermeer’s day, many colors could not be reached in one step. When Vermeer wanted a warm, golden yellow, for instance, he first had to paint an opaque layer of lead-tin yellow, which by itself is whitish and cold. When that dried, he put on a glaze with transparent gold ochre and thus got the desired effect. “Nowadays you just use cadmium dark yellow,” says the painter and art historian Diederik Kraaijpoel, “and you get the right hue immediately.”
Finally came a protective layer of varnish, made from tree resin. All the many stages, and of course the process of painting itself, were finicky and time-consuming. The rabbit glue layer and then the gesso and then the oil-priming layer each had to dry, for example, and then each had to be smoothed with a pumice stone or a piece of sharkskin. Haste or sloppiness would soon make for a cracked and broken painting, but not even the most painstaking care could head off the cracking problem altogether.
When a painting is subject to changes in temperature and humidity, which is almost bound to happen sooner or later, it begins to expand and contract. Canvas itself copes well with changing conditions because it has some give to it. One reason, in fact, that artists began painting on canvas in the first place was that canvas, unlike wood, neither cracked nor warped. (Canvas was lighter and cheaper, too, and better suited to huge paintings.) But as flexible as canvas is, eventually its expanding and contracting causes trouble. And since the layers that form a painting do their best to cling to one another, and since each layer expands and contracts at its own rate, trouble in one layer tends to induce trouble in other layers.
In some ways, this is geology in miniature. The stresses and strains and zones of weakness that can rip great gouges in the natural landscape have counterparts that can make for micro-damage to an artist’s landscapes, too. “Like miniature tectonic plates, the different layers heave and tug at each other until something gives,” says Leo Stevenson, the English painter and art historian. “Sometimes the forces are deep and strong and the cracks you see on the surface come from deep down, and at other times the forces are all at the surface and all the effects are local.”
It is impossible to foresee precisely the pattern of cracking that will emerge as a painting ages. In Van Meegeren’s case, the results were even less predictable than usual. Conventional artists worked with paints whose properties had been observed for centuries; Van Meegeren painted with strange, plastic-like paints of his own invention. Ordinary paintings hung in comfortable rooms where the heat and humidity stayed within fairly narrow bounds; Van Meegeren planned to cook his masterpiece in an oven.
What was a