The manufacture of mineral and lake pigments

by Josef Bersch

Reactions of the Red Pigments.

Pigment.	Hydrochloric Acid.	Caustic Soda.	Ammonium Sulphide.	On Heating.
Chrome red	Green solution, white residue soluble on largely diluting.	Yellow solution and white residue.	Turns greenish black.	Fuses.
Red lead	Chlorine is evolved, white residue.	Almost unchanged.	Turns black.	Turns yellow and finally melts.
Ferric oxide pigments	Slowly dissolve to yellow solution.	Unaltered.	Slowly blackened.	Become dark blackish brown.
Antimony vermilion	Dissolves with evolution of sulphuretted hydrogen.	Dissolves to colourless solution.	Becomes darker, partially soluble.	Melts.
Mercury vermilion	Unaltered.	Turns yellowish.	Unaltered.	Volatilises, sulphur dioxide evolved.
Mercuric iodide	Dissolves to colourless solution.	Dissolves to yellowish solution.	Blackened.	Fuses and then volatilises.
Realgar	Unaltered.	Dissolves to colourless solution.	Dissolves to yellow solution.	Volatilises.

On Heating on Charcoal:—Chrome red and red lead give lead beads in the reducing flame. The former gives a red mass when fused with soda, which dissolves to a yellow solution.

Ferric oxide pigments become darker, but give no incrustation.

Antimony vermilion burns with production of sulphur dioxide and white fumes without smell when heated in the oxidising flame; when fused with soda before the blowpipe, it gives a white brittle bead of metallic antimony.

Vermilion volatilises in the oxidising flame and gives a smell of sulphur dioxide.

Mercuric iodide readily fuses and volatilises.

Realgar volatilises. When heated with soda in the reducing flame, white fumes with an odour of garlic are produced.

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 blue	Dissolves to yellowish-green solution.	Blackened.	Blackened.	Blackened.
Ultramarine	Rapidly decomposed with evolution of sulphuretted hydrogen.	Unchanged.	Unchanged.	Unchanged.
Smalts	Almost unaltered, greenish solution on long boiling.	Unchanged.	Blackened.	Fuses at a high temperature.
Cobalt blue	Unchanged.	Unchanged.	Unchanged.	Infusible and unchanged.