PIGMENTS 151
have for the purpose some of the waste potash over which he had distilled in
process of purification some of the animal oil with which he was then working
(DippePs oil—a distillation product of bones and other animal matter which
consists chiefly of pyridine and pyridine bases). With this alkali Diesbach got,
in place of the expected red pigment, a blue one. He told Dippel, who realized
that the formation of the blue color was the result of the action of the spent alkali
upon the iron vitriol. Dippel had prepared his animal oil from blood. (The calcina-
tion of the blood with alkali had formed potassium ferrocyanide, which was the
reagent that had reacted with iron vitriol under oxidizing conditions to form
Berlin blue.) Kopp goes on to say that the preparation of Berlin blue was kept
secret until the Englishman, Woodward, published it in the Philosophical Trans-
actions for 1724. It was soon demonstrated that the blue could be prepared from
other animal remains (nitrogenous substances) as well as from blood. (In German,
the word, * BlutlaugensabJ is still in use, however, for potassium ferrocyanide.)
Beam, in his short historical introduction to the preparation of Prussian blue,
says (p. 85) that Diesbach communicated his discovery to a French pupil, De
Pierre, who later started making this pigment in a small way in Paris; hence, the
name, * Paris blue.' He adds that Wilkinson in London next commenced manu-
facturing it, and that gradually more and more color firms took up its production.
It must have been well known all over Europe by 1750. The earliest painting on
which De Wild reports it (p. 33) is one by J. E. La Farque, dated 1770, and it is
quite commonly found on late XVIII century and XIX century works.
Pumice (and pumicite) is a light, porous stone or natural vesicular glass of
volcanic origin, and consists of silicates of aluminum, sodium, and potassium (see
Ladoo, pp. 455-464). Ground pumice is a light gray or warm white, gritty powder.
Under the microscope, particles appear like broken glass, with the rounded
surfaces of broken bubbles appearing prominently. Much that is produced com-
mercially conies from the Lipari Islands off the coast of Sicily. It is widely em-
ployed as an abrasive and polishing agent. It is put in certain types of paint,
particularly that for masonry, where its open cellular structure allows air dif-
fusion. Being a volcanic ash, pumicite is a fine powder or dust composed of sharp,
angular grains of volcanic glass of about the same composition as pumice. It is used
extensively in cleaning powders.
Purree (see Indian Yellow).
Quartz (see Silica).
Quercitron Lake (yellow lake, flavine lake) is a yellow coloring matter made
from the inner bark of a species of oak, Quercus tlnctona^ that is indigenous to
North America. The coloring principle is quercetin or tetrahydroxyflavonal,
CisHioOr. The bark is extracted with water and the lake is made by adding alum
and precipitating with chalk (see Perkin and Everest, pp. 628-629). It is soluble
in water and in alcohol, but forms a yellowish brown solution with alkalis and is
decolorized by mineral acids. Yellow lakes of this nature are rapidly faded by