THE FORMULA FOR THE LEAD AND WAX MEDIUMS OF THE VENETIANS

GIORGIONE, TITIAN, TINTORETTO

    THE BLACK OIL, which seems to have been the invention of Giorgione, was the basis of the technique of the Italians of the High Renaissance, and of their successors down to the early part of the nineteenth century..

    It can be made with white lead (basic carbonate), or with calcined white lead (massicot or protoxide) or with litharge (oxide).'The procedure is this (all measurements are given by weight). Place in a bowl: I or 2 parts (or 3-10 Grammes) of lead or litharge 20 parts (or I00 grammes) of raw linseed or walnut oil These must be ground and mixed in the same way as for Antonello's medium. Place the receptacle containing the mixture over a low fire (protected by the asbestos mats, mentioned in previous formulas) and stir with a spatula, from time to time, during the cooking..

     If white lead is used, it will be seen in following the operation with a thermometer that the oil will begin to foam at about I00 degrees centigrade. This foam is often very abundant and this is due to the presence of water in the lead (which is hydrated). This phenomenon does not occur with litharge..

     Between 180 and 200 degrees centigrade, the oil begins to smoke and to become brownish in color. This is the sign of the beginning of its combination with the lead. The litharge, more than the white lead, has a tendency to agglutinate at about I50 degrees, and the spatula will stick in it at the bottom of the vessel. Towards 2I0 degrees, however, this deposit softens and it will finally mix with the oil at about 230 degrees. Towards 250 degrees, the oil takes on the brown

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