Red, Yellow, and Blue should first be dealt with, and _for practical work_ each pupil should be supplied with three water-colour pigments closely corresponding in hue to the standardized glasses, viz., Crimson Lake, Lemon Yellow, and Cobalt Blue; also with a piece of white paper ruled into six small rectangular spaces corresponding to the little windows of the apparatus.
As each colour is demonstrated by means of the glass in the apparatus, each pupil should paint the corresponding pigment in its proper place on the paper.
The little shutters being placed in all the six little windows, remove the top left-hand shutter and insert a deep _Red_ glass, thus showing
=Red.=--The pupils will name this and then paint the corresponding colour on their papers.
Next, remove the shutter below the first one, and insert a _Yellow_ glass of the same numerical value as the Red one, thus showing
=Yellow.=--The pupils will name this and then paint the corresponding colour on their papers.
Now remove the shutter next below and insert a _Blue_ glass of the same numerical value as the Red and Yellow ones, thus showing
=Blue.=--The pupils will name this and then paint the corresponding colour on their papers.
+--------+--------+ | 1 | | | | | | RED | | | | | +--------+--------+ | 2 | | | | | | YELLOW | | | | | +--------+--------+ |3 | | | | | | BLUE | | | | | +--------+--------+
There are now exposed to view the three colours which are by artists commonly called primaries, but it will be found convenient to term Red, Yellow, and Blue the _Dominant_ colours of this system.
The second step is to show how the three secondary or subordinate colours are derived or developed.
Remove the top right-hand shutter and insert a deep Red and a deep Yellow glass of equal depth, showing the pupils that these two colours combined in equal proportions develop
=Orange.=--The pupils will name this, and will then mix their Red and Yellow pigments to obtain a similar Orange which will be painted in its proper place on their papers.
Now remove the shutter next below and insert a deep Yellow and a deep Blue glass of equal depth, showing the pupils that these two colours combined in equal proportions develop
=Green.=--The pupils will name this, and will then mix their Blue and Yellow pigments to obtain a similar Green which will be painted in its proper place on their papers.