Preparation of the Painting: Support, Sizing and Grounding

Of all 35 surviving Vermeer's, only two works, the Girl with a Flute and Girl with a Red Hat were not painted on canvas but on thin oak (?) panels. However, in Vermeer's death inventory of 1676 there were listed 10 unpainted canvases and 6 unpainted panels in his studio which indicates that the artist's preference for canvas was not so accentuated as the proportions of his surviving paintings would lead us to believe.

Although canvas as a support for painting was know to the ancients, it became widely used in Italy for oil painting by the end of the 15th century. Until then, both tempera and oil painting had been done primarily on wood panels. The word canvas does not refer to any specific material in the field of textile fabrics, it is applied to number of closely woven materials of relatively course fibers. Linen is preferred for its superior strength. It tears with great difficulty. It is also less hygroscopic than other fabrics which instead draw moisture from the air and, upon drying, throw it off and are in a sort of continual expansion and contraction in which the dry pigment cannot participate. This causes the paint to crack severely.

Canvas has various advantages over panel: it is easily transportable, it is far less laborious to prepare, and it can be used to make paintings of far greater dimensions. The Marriage of Cana, the largest known oil painting in the world, by Paolo Veronese, measures an astounding 22 x 32 1/2 ft. (666 x 990 cm.) The tooth and spring of the prepared canvas facilitate a more rapid and expressive execution. It is also possible to effectively use greater quantities of paint and achieve more varied aesthetic solutions. At the same time canvas also permits the painter to obtain a great degree of fine detail although not as much as a perfectly smooth panel. Various tones, degrees of roughness and absorption of the canvas can be achieved by altering the materials and preparation methods.

Unless treated, canvas is very absorbent and quickly swallows up the oil content of the paint causing it to sink into the fabric. The final chromatic effect of the picture would be impossible to calculate and the roughness of the raw canvas world destroy any illusionistic effects. Canvas must first be properly stretched, sized and grounded before painting.

It is now believed that many, if not most, seventeenth-century painters did not prepare their own canvases but bought them ready-made from specialized colourmen. The sizes may sometimes be associated with local units of measure. The width of a roll of cloth was governed by the width of the 100m: most looms in Twente and Brabant, the main sources for canvas in the Northern Netherlands were two ells (ca. 138 cm) wide, whereas 100m widths of Italian canvases tend to range between 106 and 110 cm.

Format and Stretching

Vermeer's paintings are often similar in size in different periods. "This cannot be due to chance, rather it suggests that Vermeer used standard sizes."¹ The 1: 1:14. width to height ratio he generally employed is very nearly square. The square format is the most visually reassuring and stable of all geometrical forms and was used widely in the Netherlands although painters have always avoided using the perfect square since it tends to have a stifling effect on the inherent expressive content of a work of art. It has been noted that the first historical paintings are quite large in scale in respects to his interiors.

Vermeer generally attached his canvas directly on the final stretcher contrary to the practice of attaching it onto the oversized strainer. This later method was a widely used and can often be observed in representations of painters in their studios (right). Although this method was employed principally for preparing the canvas, some painters also executed their works while they were still on the strainer. The function of these oversize strainers must have been to provide a simple and effective way of stretching and restretching a canvas to take up slack. Today's familiar expandable stretchers which take up the lost tension by means of wedges inserted in the corners became common only in the 1750s.

Vermeer's Guitar Player, unique among seventeenth-century canvases, is still on its original strainer with the original square wooden pegs used to fix the canvas to the sides of the strainer.

Sizing

animal skin glue with water
makes medium strength jelly

Sizing seals effectively the canvas against ground and paint layers, both of which contain drying oils that would be damaging if applied directly. Sizing was made of clippings of rabbit hide, pig-skin or parchment which presents itself in the form of thin brittle sheets or course crystallized grains. Size is first soaked in cold water where it swells considerably. It is then heated in a double boiler until it becomes completely fluid. The warm glue, about the consistency of honey, is spread on the taught canvas with a palette knife with quick energetic strokes forcing it to penetrate as deep as possible into the open pours. Animal skin glue must never be brought to boiling temperature as it is very liable to crack shortly afterwards. The presence of animal skin glue can be detected by laboratory analysis for its high protein content. The presence of size, an organic material, in Vermeer's paintings is indicated by its high protein content.

Grounding

After the sized canvas was dry, it was sanded with a pumice stone and grounded. Grounding, or priming as it is usually called today, provides the final surface suitable for painting. Grounding must produce a smooth surface that can be easily painted upon, it must be hard but not brittle (which causes cracking) and last of all it must be porous enough to allow the oil paint to adhere permanently but not too absorbent as to suck out the oil from the layers of oil paint and cause it to detach.

The Dutch and Flemish often prepared their canvases with two layered ground. Generally, the first coating of the Netherlandish double-ground, painted directly on the canvas, consisted of a mixture of earth pigments, and may also contain fair amounts of palette scrapings or the sediments from the jar of oil used to clean brushes. This produces a dirty grayish color, which may contain a large variety of pigments from the cleansing oil; its purpose was simply to provide a smooth surface economically. The second ground layer, or imprimatura, usually consisted of a mixture of lead white and carbon black providing a flat gray tone: to ensure optical neutrality, a small amount of iron oxide reds and other earth pigments was almost always added to the mixture, thus preventing 'Raleigh scattering', an optical effect which makes a mixture of charcoal black and lead white over a darker priming appear a harsh, cool, bluish gray. AlI imprimature of Northern European seventeenth-century paintings have some iron oxide reds, ochres and umbers mixed in with charcoal and lead white.

Vermeer generally used light colored grounds composed of chalk (a filler), linseed oil, white-lead and various combinations of coloring pigments. For example, the ground of the Woman Holding a Balance contains chalk, white-lead, black and an earth pigment, most likely brown umber. The ground mixture was applied in one layer. The grounded canvas had a warm buff tone that can be seen in various areas of the painting where little or no paint was applied. It would seem that Vermeer prepared his canvas in the conventional manner.

The Value of Colored Grounds

Painters were aware that the tone of the ground strongly influences the perception of the tone and hue of the pigments which were applied to it. Thus, the final overall tone of the picture was effected, especially in the shadows where thin layers of transparent paint were generally employed. Dark toned canvases greatly aid the rendering of shadowed areas but require repeated layers of lighter paint to represent the strongly illuminated areas.

On the other hand, a ground which is very light obviously does not evidence light tones which painters use in abundance. On a pure white ground any color applied would be darker than the ground allowing the artist to paint in only one direction. Pure white canvas grounds were rarely used. It is very difficult to harmonize a strongly colored paints of such grounds. While on a white ground all tonal shades have to be applied deliberately, a tinted ground acts as a middle tone by itself. For these reasons neutral or warm light grays were used by Vermeer as well as many other Dutch painters of the time, although he known to have once used a white ground only once at the beginning of his career and a strongly reddish toned in the Love Letter.

Ground material was applied with a palette knife in one or two layers.