This section is from the book "Chromatography; Or, A Treatise On Colours And Pigments, And Of Their Powers In Painting", by George Field. Also available from Amazon: Chromatography, or A Treatise on Colours and Pigments, and of Their Powers in Painting.
Constant White , permanent white, or Bart/tic white, is a sulphate of barytes, and when well prepared and free from acid is one of our best whites for water-painting, being of superior body in water, but destitute of this quality in oil.
As it is of a poisonous nature, it must be kept from the mouth; - in other respects and properties it resembles the true pearl white. Both these pigments should be employed with as little gum as possible, as it destroys their body, opacity, or whiteness; and solution of gum ammoniac answers better than gum arabic, which is commonly used: but the best way of preparing this pigment, and other terrene whites, so as to preserve their opacity, is to grind them in simple water, and to add toward the end of the grinding sufficient only of clear cold gelly of gum tragacanth to connect them in a body, and attach them to the paper in painting. Cold starch, or other vegetal or animal gelly, will answer the same purpose. Barytic white is seldom well purified from free acid, and, therefore, apt to act injuriously on other pigments.