Reactions of the Blue Pigments.

Pigment.Hydrochloric
Acid.		Caustic
Soda.		Ammonium
Sulphide.		On Heating.
Prussian, Chinese,
Paris, Turnbull’s,
 and
Brunswick blue		Dissolve to green
solution, then yellow.		Decolourised,
brown residue. 		Liquid yellowish
green.		Blackened.
Mountain blueDissolves to
yellowish-green
solution.		Blackened.Blackened.Blackened.
UltramarineRapidly decomposed
with evolution of
sulphuretted hydrogen. 		Unchanged.Unchanged.Unchanged.
SmaltsAlmost unaltered,
greenish solution on
long boiling.		Unchanged.Blackened.Fuses at a
high temperature.
Cobalt blueUnchanged.Unchanged.Unchanged.Infusible and
unchanged.

On Heating on Charcoal:—Prussian, Chinese, Paris, Turnbull’s and Brunswick blue are turned black, the residue colours the borax bead pale brown in the oxidising flame, and pale green in the reducing flame.

Ultramarine is unaltered at a high temperature.

Smalts, on long heating in the reducing flame with borax, gives a dark blue bead.

Cobalt blue is infusible; it colours the borax bead blue. The bead loses its fine colour on long heating in the reducing flame.

Mountain blue is blackened before the blowpipe. When the residue is moistened with hydrochloric acid and again heated, the flame is coloured bright green. When fused with borax in the oxidising flame, an emerald green bead is formed.