Blue Ochre

which has been improperly called Native Prussian Blue, is a native

hydrated phosphate of iron of rare occurrence, found with iron pyrites

in Cornwall, and also in North America. What Indian red is to the colour

red, and Oxford ochre to yellow, this pigment is to the colour blue,

being sober and subdued rather than brilliant. It has the body of other

ochres, more transparency, and is of considerable depth. Both in water

and oil it works well, dries readily, and does not suffer in tint with

white lead, nor change when exposed to the action of strong light, damp,

or impure air. As far as its powers extend, therefore, it is an eligible

pigment, though not generally employed nor easily procured; it may,

however, be artificially prepared. Answering to similar acid tests as

ultramarine, it is distinguished therefrom by assuming an olive-brown

hue on exposure to a red heat.

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