CHAPTER XV

COLOURS: THEIR PREPARATION AND USE

It is practically needless to say that the colours used for illuminating are water-colours. These are sold by the artists’ colourmen, ready prepared, in three different forms, _viz._, in cakes, pans, and tubes. These consist of powder colour ground with gum arabic, or senegal (a brown variety of the same gum), to which a portion of honey and glycerine is added.

The best prepared colours are undoubtedly those sold in the form of cakes, as they are the purest. The other forms contain a considerable amount of glycerine, which does not improve the colour, but enables them to be kept moist for quite a long time--a greater advantage to the artists’ colourman than to the artist.

Tube colours contain more glycerine than those sold in pans. The great advantage, however, that tube colours possess is their convenience. A small quantity of clean colour can be squeezed out and the cap replaced on the tube, thus keeping the rest of the colour free from dust. The admixture of so much glycerine with the colour, however, often prevents it from drying quite flat when used as body colour.

One word of warning may be useful here: gum should not be mixed with water-colours. This is often recommended in books on illumination, but it is not only unnecessary but it entirety spoils the appearance of the colour. There is always quite sufficient gum mixed with the colour, and there is nothing specially beautiful about the shiny appearance caused by an excess of gum in the colour.

Without a doubt the best colours for the illuminator to use are powder colours. They are mixed with gum arabic and water. Care should be taken to get the right quantity of gum mixed with the colour. If there is not sufficient to bind the colour it will rub off when dry, while, on the other hand, if there is too much, it will dry patchy, and if very much in excess it will present a shiny appearance. Experience will soon show the exact amount necessary.

One very great objection that is often urged against the use of powder colours is their inconvenience, but if these are prepared in the manner described below they should not be more inconvenient to use than the ordinary ready-prepared water-colours.

For illuminating, where the work is required to be lasting, none but permanent colours should be used; but when making designs which are for temporary use only it is foolish to use expensive colours like aureolin and cadmium yellow when the same effect can be obtained with the various shades of chrome yellow, which is much cheaper, although notoriously fugitive.

It is best to buy the colours ready ground. A china slab or a piece of plate glass may be used to mix the colours on, or the back of a large white plate might serve in lieu of these. When it is necessary to grind the colour a muller is used for this purpose. (See Fig. 29.)

Gum arabic is prepared in a very simple manner for mixing with colours. Some pieces of this gum are placed in a wide-mouthed jar and covered with cold water. It should be given a stir occasionally, and the following day it will probably be dissolved. It may be strained through muslin if necessary. A few drops of carbolic acid added to it will prevent this solution from becoming sour. It is as well also to provide a loose-fitting cover for the jar to keep dust from the gum.

For mixing the colour a palette-knife is required. A little of the powder colour is placed on the slab and mixed with the palette-knife to a stiff paste with water and a little gum. A glass tube may be used to take the gum from the jar. If this tube is placed in the jar of gum, and the finger placed over the top of it, a small quantity of gum can be easily removed and may be dropped on to the slab by removing the finger. (See Fig. 29.) This is a much better method than dipping the palette-knife into the gum, as this is very likely to get contaminated with the colour if this is done.

It is not advisable to mix the colour too thinly with water before adding the gum, as one of the effects of the gum is to make the colour flow much easier, and if there is a fair quantity of colour on the slab it is liable to flow over the edges.

After it has been well mixed up with the palette-knife it should be tested to see if it has sufficient gum in it. The student should take a clean brush and paint a small square with the colour on a piece of paper. When this is quite dry it is very easy to tell if it has the proper quantity of gum in it. As mentioned before, if it has too much the colour will look patchy or shiny. To find out if there is enough gum in it, take a small piece of rough paper and rub the patch of colour vigorously with it; if there is insufficient gum to bind the colour it will rub off on to the paper; if there is too much gum, more colour should be added; while, on the other hand, if there is not enough a little more should be mixed with it.

When painting a fresh square of colour for testing purposes it is essential that the brush should be thoroughly washed before painting the new patch. If this is not done the result will be that the colour will be mixed with that already in the brush, and the test will not be a true one. Another important thing is to see that the colour is well mixed with the gum, otherwise one is very liable to get one brush full of colour that is nearly all gum and another with insufficient gum in it.

When the colour is well mixed up with the right quantity of gum it should be thinned out with water and is then ready for use. It should be placed in little saucers, which may be obtained from any artists’ colourman. A small square of glass may be placed over the saucer to prevent the evaporation of the water from the colour, as, if left exposed to the air, this will soon dry quite hard. If it is desired to keep the colour moist for any considerable time, a small quantity of glycerine and honey should be added to it. The colour, however, does not work so well when used as body-colour if this is done.

The following is a good method of keeping body-colour in a convenient form. The colour should be painted on large pieces of glass or slabs of porcelain and allowed to get perfectly dry. It can then be scraped up in the form of a fine powder. An old chisel-knife, or a broken palette-knife, makes a good scraper. This powder requires only a little water to be added to it and the colour is ready for use. It dissolves very quickly in water to form an easy-flowing colour, much superior to colour that has glycerine and honey added to it to keep it moist. Especially is this the case when working on vellum. It dries with a dull, velvet-like surface which shows in strong contrast to brightly burnished gold. If the colour, when scraped up, is not very finely divided it should be rubbed up, in its dry state, on the slab, with the palette-knife or muller, until it is quite fine, as the finer the powder the more quickly will it dissolve.

A complete set of colours for illuminating may be prepared in this way and put into small bottles until required. No gum should be added when using them, as each small grain of colour has its own portion of gum which binds it to the surface on which it is painted.

When it is required to use any of the colours prepared in this way, a small quantity of the powder should be placed in a small saucer and a little water added. It should then be worked up with the finger-tip until it is fluid enough to work well with the brush.

Colours prepared in this way work very well also in the pen, vermilion especially working very well indeed. It is not advisable to use a brush to mix the colour up with, as this method not only quickly spoils a brush, but also it does not mix the colour up nearly so well as the finger-tip.

If a little colour is left in the saucer after using it, it can easily be moistened up again with a little water. It is not, however, advisable to mix up much more than is required, as it dries rather hard and requires soaking some little time if a considerable quantity is left to dry.

When mixing colours in this way it is as well to label carefully the bottles in which the colour is stored. If this is not done, one is very liable to mistake a fugitive colour for a permanent one, and _vice versâ_. Cadmium yellow may easily be mistaken for chrome yellow, and crimson Lake for permanent crimson.