Wallace Seymour Smalt, blue-glass, genuine. Sky blue. Stoke-on-Trent Bespoke Oil Paint

Smalt, blue-glass, genuine. Sky blue. Stoke-on-Trent PB 32

Saxon blue, royal blue. K,Co (Al) – potash silicate (glass) with cobalt oxide.

Blue glass powder.  Glass-makers took these minerals and found that, when heated to high temperatures, they could be used to colour glass blue.

Smalt is also associated with the glass-makers of Murano, Venice and was used in many Venetian paintings during the 1600s, most often admixed with lead white, to create sky colours.

Weak when admixed with other colours; the transparency of the material causes it virtually to disappear. Deep blue with a purple tinge. Transparent. Glass.

In oil, the blue colour becomes almost invisible: glass has a similar refractive index to dried linseed oil, as a consequence the eye does not register the colour. This phenomenon is only observed in dried paint films: when the paint is freshly applied, the blue colour remains visible. This effect can be countered by admixing smalt with a little white, which breaks up the way that light transmits within the paint film.

Very fast to dry. Smalt has a catalytic effect on oil, indeed it has often been cited as a siccative agent for drying vegetable oils.