| Red | 8 | parts of size-solution (by weight) to | 1 | part of | vermilion. |
| Yellow | 6 | ” ” | 1 | ” | chrome yellow. |
| White | 5 | ” ” | 1 | ” | flake-white. |
| Blue | 3 | ” ” | 1 | ” | blue-smalt, fine. |
| Black | 12 | ” ” | 1 | ” | lamp-black. |
Whichever of these colours is made use of must be levigated in a mortar with the addition of a very small quantity of water until every lump of colour or foreign matter is reduced to the finest state possible, otherwise in the process of injecting it will most likely be found that some of the small channels have been closed and the progress of the liquid stopped. When this fineness of particles is attained, warmth sufficient to render the size quite fluid must be used, and the colour added gradually, stirring all the time with a rod. It may be here mentioned that where one colour only is required, vermilion is, perhaps, the best; and blue is seldom used for opaque objects, as it reflects very little more light than black.
12. When it is wished to fill the capillaries (the minute vessels connecting the arteries with the veins), the “Micrographic Dictionary” recommends the colouring matter to be made by double decomposition. As a professed handbook would be, perhaps, deemed incomplete without some directions as to the mode of getting these colours, I will here make use of those given in that work. For red, however, vermilion, as above stated, may be used; but it must be carefully examined by reflected light to see whether it be free from all colourless crystals or not. It must first be worked in a mortar, and then the whole thrown into a quantity of water and stirred about; after leaving it not longer than a quarter of a minute, the larger portions will settle to the bottom, and the liquid being poured off will contain the finer powder. This may then be dried slowly, or added to the size whilst wet in the manner before advised.
13. Yellow injection.—To prepare this, take—
| Acetate (sugar) of lead | 380 grains. |
| Bichromate of potash | 152 ” |
| Size | 8 ounces. |
Dissolve the lead salt in the warm size, then add the bichromate of potash finely powdered.
Some of the chromic acid remains free, and is wasted in this solution, so the following is given:—
| Acetate of lead | 190 grains. |
| Chromate of potash (neutral) | 100 ” |
| Size | 4 ounces. |
The first of these has the deepest colour, and is the most generally used.
14. White injection.—This is a carbonate of lead:—