Illuminated manuscripts in classical and mediaeval times, their art and their technique

by J. H. Middleton

Vitreous pigment.

Vitreous pigment.Smalto blue is simply a powdered blue glass or vitreous enamel, coloured with an oxide or carbonate of copper. Vitruvius (VII. xi. 1) describes the method of making it by fusing in a crucible the materials for ordinary bottle-glass, mixed with a quantity of copper filings. The alcaline silicate of the glass frit acts upon the copper, which slowly combines with the glass, giving it a deep blue colour. The addition of a little oxide of tin turns it into an opaque blue enamel, which when cold was broken up with a hammer, and then powdered, but not too finely, in a mortar.

Smalto blue is largely used for the simple blue initials which alternate with red ones in an immense number of manuscripts. The glittering particles of the powdered glass can easily be distinguished by a minute examination. Like the ultramarine, the smalto blue is always applied in a thick layer.

The monk Theophilus (II. 12), who wrote during a period of some artistic and technical decadence, the eleventh century, advises the glass-painter who wants a good blue to search among some ancient Roman ruins for the fine coloured tesserae of glass mosaics, which were so largely used by the Romans to decorate their walls and vaults, and then to pound them for use.

German blue.

German blue.Azzurro Tedesco or Azzurro della Magna, German blue, was much used by the illuminators as a cheap substitute for ultramarine. This appears to have been a native compound of carbonate of copper of a brilliant blue colour. It was occasionally used to adulterate the costly ultramarine, but this fraud was easily discovered by heating a small quantity of the pigment on the blade of a knife; it underwent no change if it was pure; but if adulterated with Azzurro della Magna it showed signs of blackening[^[271]].

Indigo.

Indigo.Indigo blue. The above-mentioned blues are all of a mineral character, and are durable under almost any circumstances. To some extent however the vegetable indigo blue was also used for manuscript illuminations, both alone and also to make a compound purple colour.

Method of using dyes.

Method of using dyes.Colours of all kinds prepared from vegetable or animal substances required a special treatment to fit them for use as pigments in solid or tempera painting. Though indigo and other colours of a similar class are the best and simplest of dyes for woven stuffs, yet they are too thin in body to use alone as pigments. Thus both in classical and mediaeval times these dye-pigments were prepared by making a small quantity of white earth, powdered chalk or the like absorb a large quantity of the thin dye, which thus was brought into a concentrated and solid, opaque form, not a mere stain as it would otherwise have been.