Origin

The sources of yellow lake are numerous, but the best kind is obtained from quercitron bark from Quercus tinctoria, Qu. nigra, and Qu. citrina, three species of North American oak. A hot-water decoction is made, and this is precipitated by a solution of alum and dilute ammonia. A richer yellow pigment is obtained by extracting the powdered bark and alburnum with boiling dilute sulphuric acid instead of with water. The original colouring matter of the bark (quercitrin) is thus changed into a more stable compound known as quercetin. The former substance is a glucoside, the latter has the character of an acid; both may be converted into lakes by bringing them into contact with precipitating or precipitated hydrate of alumina. Yellow lake was formerly made from the fruits of various species of buckthorn, known as Persian, Turkish, or Avignon berries. The species yielding these fruits are Rhamnus infectorius, R. oleoides, R. saxatilis, R. amygdalinus, R. catharticus. The bark of R. frangula and of R. catharticus also yields a yellow pigment. 'Stil de grain,' and several of the continental yellow lakes, are made from the above-named berry.

Italian pink, Dutch pink, and deep yellow madder are names usually given to the richer yellow lakes of quercitron, although some of these pigments are occasionally prepared from Turkish or Avignon berries.

Beautiful and useful as many yellow lakes undoubtedly are, they should be rigorously excluded from the artist's palette. In oil most of them are very bad driers, as well as fugitive: in water-colour they generally lose nine-tenths of their colour within two years of exposure to sunlight: the residual stain is ultimately of a bluish-grey.

The following observations as to the behaviour of several members of this group, on exposure for two years to sunlight, apply to the colours as ground in oil, and as mixed with flake-white in tint:

Name

In Oil only

With

Flake-white

Original

Intensity=10

Laque Robert - hellgelb - - -

Lemon yellow -

Pale straw - -

2

Residual Intensity.

Laque Robert - dunkelgelb - - -

Deep lemon -

Stone - - -

4

Laque brun-jaune -

Salmon - -

Pale rose - -

7

Laque brun-foncÚ -

Yellowish-grey

Smoke-grey -

8

Pale yellow madder -

Pale orange -

Pale buff - -

7

Deep yellow madder -

Greyish salmon

Pale greyish pink

6

The same pigments used as glazing colours over flake-white have faded to about the same extent, but their change of hue is, in one or two cases, rather less marked.

The so-called brown pink is usually a deep quercitron lake, although it was formerly made from the berries of one of the kinds of buckthorn (Rhamnus) previously named. I have never met with a specimen of it which would stand a year's exposure to sunlight without suffering almost complete change or loss of colour both in water and in oil. And it further presents the awkward effect of becoming ultimately of a cool bluish-grey hue, a change particularly unfortunate when it has been freely used to represent foreground vegetation, or the golden lights on the near foliage of trees. Yet I am bound to confess that in Mr. W. Simpson's fifteen years' trial of certain water-colour pigments, the brown-pink has suffered comparatively little alteration. Had a portion of the original cake-colour employed been preserved for examination it might have been possible to have discovered the cause of this anomalous behaviour of the particular specimen in question.