Ochre Browns

The slight affinity of sulphur for yellow ochre, with its merely

temporary effect thereon, was observed in the eighth chapter, where

allusion was made to the action of sulphuretted hydrogen and sulphide of

ammonium on the earth. Sulphur alone, and in the dry state, ignited with

yellow or other native ochres converts them into browns, varying in hue,

and of greater or less durability. Those browns, however, which we have

made by this process, although standing well in a book, have not

withstood exposure to light and air. They have all become pale, whitish,

or of a drab cast, evidently through the oxidation of the sulphur, or

rather the sulphide of iron formed during the calcination. Practically,

therefore, ochres have an antipathy to sulphur, moist or dry, by itself

or in combination; and are, so to speak, the disinfectants of the

palette. Ever waging war against sulphurous vapours, the native earths

serve to protect a picture from the damaging influence of impure air,

whether they be used alone, or employed in admixture with such pigments

as are injured thereby.

Nickel Brown Olive Oxide Of Chromium facebooktwittergoogle_plusredditpinterestlinkedinmail