(Smalte, smaltino, starch blue, cobalt glass)


Origin, History and Characteristics

cermaic tile with smalt
Ceramic tile painted with smalt pigment

Smalt is ground blue cobalt-containing glass. It was first described by Borghini in 1584. Cobalt oxide obtained was melted together with quartz and potash or added to molten glass. When poured into cold water, the blue melt disintegrated into particles which were then grounded. Several grades of smalt were made according to cobalt content and grain size. In European painting it was initially used as a substitute for expensive natural ultramarine. Smalt has been historically important as a pigment in painting, pottery, for surface decoration of other types of glass and ceramics, and other media. It is colored to a deep powder blue hue using cobalt ions derived from cobalt oxide.

As smalt is a glass, its particles are transparent, and its covering power as a pigment for fine painting is low. Therefore it must be coarsely ground for use as a pigment. When used in oil medium, it has a tendency to settle under the paint film (causing it to yellow in time) and streak down perpendicular surfaces. Smalt was frequently bound with a protein binding medium (usually parchment or animal skin glue) as stated in several contemporary treaties to prevent it from being altered by the yellowing of the oil film. The gelatinous nature of the glue medium keeps the particles suspended until the paint becomes dry. Although smalt is known to fade, the degree to which this occurs can vary even within the same painting.

Smalt was frequently used by painters in the blue skies and distant mountains. It was popular for its low cost and its manufacture became a specialty of the Dutch and Flemish in the seventeenth century. Smalt is a very good dryer and was admixed in small quantities to dry other slower drying pigments..

Smalt in Vermeer's Painting

In several early paintings by Vermeer smalt was found, but mostly as an admixture to other pigments in deep layers. The smalt found in Vermeer's paintings is very coarse grained. There is smalt in the lighter area of the walls of A Maid Asleep together with azurite, ocher, brown ocher and naturally the principal component, white-lead and in the underpainting of the blue area of the carpet. An upper area contains instead, azurite and natural ultramarine. Smalt may also be found in The Procuress in both the light white areas and as a component of the green paint with lead-tin yellow.

There is extensive use of smalt in Diana and her Companions in the brown undermodeling where it is bound in a protein medium, it is also in the flesh tones as well as in the thistle, the rock and the dog's white fur.

In a few of his earlier works Vermeer used small quantities of smalt to tone down the white areas of pure white instead of black which produces a sullen matt gray effect. The artist later used natural ultramarine for the same purposes in works such as the Young Woman with a Water Pitcher.

Vermeer seems to have abandoned smalt after the first few early works along with complex mixtures of five or more pigments.