THE FORMULA OF VELASQUEZ
Velasquez proceeded in much the same way as the Italians, but instead of using oxide of lead to obtain his black oil, he used verdigris, which comes from copper. The ingredients used in this formula (by weight) are:
1 part of finely pulverized verdigris.
20 parts (approximately) of raw linseed or walnut oil.
These are cooked over a low fire and stirred from time to time. In cooking, the contents of the vessel at first have a greenish color and are fairly agitated, then towards 15o degrees centigrade, they become reddish, and on continuing, this red tone disappears to give place to a coffee color, very close to that of the black oil of Giorgione. It should be left to stand for several days and the deposit should never be disturbed or shaken. It is better to filter and re-bottle it, as is done with the black oil made with lead (described in previous formulas). All the colors except white are ground with it. Wax is added to the colors as with the Italian technique. The dilution of the colors is made either with the black oil or with black oil mixed with wax, and for special requirements--for particular minutia of detail--with turpentine. This Spanish oil has a quality of extraordinary fineness..
NOTE:: Of the other two most famous Spanish masters, El Greco used essentially the Italian medium (he is considered to have been a pupil of Titian or
Tintoretto) while Goya, born over a hundred years after Rubens had died, like his contemporaries outside Italy, could no longer discover the secret medium and painted without it, as we see from the restrained modeling and other technical characteristics of his otherwise excellent work.
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