Preparing the image: ground layers in Portuguese painting of 15th and 16th centuries – engraving and preparation

The study of the ground layers in ancient painting covers different aspects of its production stages. One of the phases, which we will explore in this text, is the adequacy of the ground layer to receive the drawing. With this aim we made an approach to the type of drawing found in some of the works studied by identifying certain technical issues established in prints from metal engraving technique, with Northern European influences. Ground layers are mostly composed of calcium sulfate, mainly anhydrite in the case of gesso grosso, with addition of calcium carbonate grains in order to smooth the surface of the drawing and painting, or dihydrated gypsum, gesso mate or "gesso sottile", which alone provides the ideal smoothness and fineness to receive the minutia of the drawn details