In order to deceive the experts, van Meegeren's forged paintings had to have a hard surface consistent with their supposed age. Conventional oil paints, made with drying oils such as linseed oil, dry very slowly and pictures painted with them take decades to achieve hardness. So it was necessary to find an alternative medium that would dry quickly and thoroughly and harden completely. Van Meegeren's solution of the problem was to use a synthetic phenolformaldehyde resin - known as Albertol or Ambertol - dissolved in a spirit such as turpentine and/or an essential (i.e., non-fatty) oil such as oil of lilac or oil of lavender, which would then be mixed with hand-ground powder pigments. (As Vermeer would have done, van Meegeren ground his own colours by hand and made his own badger-hair brushes). The resin was a thermosetting one, that is to say that when subjected to heat it would change its chemical composition permanently and become insoluble in alcohol or other common solvents.
To appear authentic, his pictures had to be painted on genuine 17th-century canvases, which meant that he had to buy a genuine, if minor, work of the period. The original painting would be partially removed with pumice stone, care being taken to retain the old network of age-crackles. Next, a so-called "levelling" layer of paint would be applied and this would form the ground for the final painting, which, when completed, would be baked in a specially-constructed oven for about an hour at a temperature of 105 degrees F. The picture would be varnished, then "distressed" so that the original age-crackle broke through to the surface. Ink would be spread over the picture to seep into the cracks and simulate the dirt of centuries. The ink and varnish would then be removed from the surface of the picture which would be re-varnished.