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.
Reactions of the Green Pigments.
| Pigment. | Hydrochloric Acid. | Caustic Soda. | Ammonium Sulphide. | On Heating. |
|---|---|---|---|---|
| Verdigris (all varieties) | Dissolves to green solution, smell of acetic acid. | Unaltered. | Blackened. | Blackened with evolution of peculiar odour. |
| Bremen green, Brunswick green | Green solution and white residue. | Unaltered. | Blackened. | Blackened. |
| Emerald green, Scheele’s green | Dissolves to greenish solution. | Gradually coloured brownish yellow. | Becomes brownish black. | Blackened and evolve garliclike odour. |
| Copper borate | Dissolves to greenish solution. | Black residue. | Becomes brownish black. | Fuses. |
| Rinmann’s green | Dissolves to rose-red solution. | Unaltered. | Blackened. | Unaltered. |
| Chromium oxide | Almost unaltered. | Unaltered. | Becomes dark dirty green. | Unaltered. |
| Chrome green lake | Becomes deeper in colour. | Unaltered | Becomes dark dirty green. | Unaltered |
| Manganese green | Dissolves to green solution. | Dissolves to green solution. | Discoloured. | Unaltered. |
| Green ultramarine | Is decolourised with evolution of sulphuretted hydrogen. | Unaltered. | Unaltered. | Unaltered. |
On Heating on Charcoal:—Verdigris, Bremen and Brunswick greens give black residues on charcoal, which produce a bluish-green bead when fused with borax in the oxidising flame.
Emerald green and Scheele’s green behave in a similar manner, but on heating evolve an odour of garlic.
Rinmann’s green gives a blue borax bead.