gesso

Gesso comes from Italian gesso (chalk, gypsum, plaster), from Latin gypsum (gypsum, plaster), borrowed from Greek γύψος (gypsos, gypsum, chalk, plaster). Gypsum is a naturally occurring mineral — calcium sulfate dihydrate — that has been used since antiquity as a building material, a sculpting medium, and a surface preparation for painting. In the Italian Renaissance workshop tradition, gesso referred specifically to the white ground applied to a wooden panel in preparation for egg tempera or oil painting. This ground was made from gypsum or chalk mixed with animal-skin glue, and it was applied in multiple thin layers — sometimes eight to twelve coats — each sanded smooth before the next was added. The resulting surface was brilliant white, perfectly smooth, and slightly absorbent: ideal for receiving the fine, precise strokes of egg tempera, and the luminous glazes of early oil paint.

The preparation of a gesso ground was one of the most labor-intensive stages of the Renaissance painter's process, and it was typically done by workshop assistants rather than the master himself. The wooden panel — usually poplar in Italy, oak in the Low Countries — had first to be prepared: joined, planed, and sometimes reinforced with battens against warping. Then the gesso grosso (coarse gesso), a rougher, more porous layer, was applied first, followed by the gesso sottile (fine gesso), polished smooth with pumice or a damp cloth. The quality of the gesso ground was a precondition for the quality of the painting on top of it: a poorly prepared surface would cause paint to crack, colors to sink unevenly, and the finished work to deteriorate. The invisible foundation determined the longevity of the visible image.

Gesso underwent a significant transformation when painting on canvas replaced panel painting as the standard support in the sixteenth and seventeenth centuries. Canvas — woven linen or hemp — is flexible and cannot receive the traditional rigid gesso preparation without cracking. Painters developed an alternative ground using white lead paint (lead carbonate mixed with linseed oil) for canvas paintings, and this ground rather than gesso remained standard for canvas painting from the Renaissance through the nineteenth century. The word 'gesso' continued to be used loosely for various preparatory grounds, but the traditional egg-bound gesso was technically limited to rigid supports. In the twentieth century, acrylic gesso — a synthetic preparation made with titanium dioxide and acrylic polymer emulsion — was developed for use on both canvas and rigid supports, and this product, though chemically different from traditional gesso, is now the most widely used ground preparation among contemporary painters.

In sculpture and decorative arts, gesso served an equally important function as a modeling medium. The gilded and painted surfaces of altarframes, furniture, and architectural ornament in Renaissance Italy were typically built up in layers of gesso applied over a wooden armature, carved or pressed into relief forms, and then gilded or painted. The elaborate cartouches, putti, and foliate ornament of Baroque picture frames were commonly made of wood covered with layers of gesso that was modeled into detail impossible to carve directly in wood. This tradition of gesso modeling — gessoed ornament — persisted through the eighteenth century and left its mark on the vocabulary of interior decoration. The word itself, through this decorative tradition, came to suggest the ornamental white surfaces of formal rooms: the gessoed walls of Venetian palazzi, the gilded gesso of church interiors.