Sepia is a fine, rich, warm, and deep colour, but must not be used too thickly ; for, like bitumen or asphaltum, it never dries in the mass—a skin forms over it, and it is sure to crack.
The excessive use of these bituminous pigments is responsible for the destruction of many of Reynolds's and Wilkie's works.
The Dutchmen, however, knew how to use them. Bituminous pigment formed the base of many of their works, particularly of the School of Teniers ; but their pictures were generally small, and no great quantity of the dangerous pigment was needed.
I have advised the use of three kinds of white. Kremser or Blanc d'Argent has not much body, but is useful to mix with other colours, where impasto is not sought after.
Flake white and the stiff white have more body, so that more solid passages of light can be realised with them.
Use fresh colours each day. There are a few reds, like Rose Madder, Vermilion, Light Red, and Indian Red, as well as Black, which may be left on the palette for a few days. They do not dry as quickly as the others, which you will do well to remove at the end of the day's work.
To avoid waste, you may transfer the paints from the palette to a sheet of glass, which does not absorb the oil like the wooden palette ; and next morning remove the " skin " that has formed over night, and put the fresh pigment that will be found under the skin back again upon the palette.
Do not starve your palette. A little experience will enable you to guess the quantities you are likely to use in the day's work. Stale or partially dry colours will hamper you. There are always enough technical difficulties to overcome.
Keep your palette scrupulously clean. It is impossible to obtain any brilliancy with a dirty palette, and luminosity is the rarest quality to attain—and one of the finest.
During the course of your work, when your sitter is resting, or at other intervals, collect with your palette knife the paint spread over the palette in painting, and make it up into two or three piles away from the centre.
These piles of colour will serve as the nuclei of greys that you may perhaps require. Then clean the centre of the palette with rag, of which a fair quantity should be at hand.
It is a good thing before actually painting to mix up a few masses of the light, half-tone, shadow, and background colours. They can be further mixed on the palette more closely to match the tones required as you proceed. This expedites the work, which is an important consideration. It encourages you also to work with a fuller brush. Such masses must not be mixed long before the work begins, or they may become partially dry and unworkable, particularly in summer time or in a very warm studio.
Good and fresh spirits of turpentine you would use as a rule for the first lay in of most work. About other mediums I shall advise you at the appropriate time.
Lay your palette in this order when you are painting in full colour direct (for the monochrome method very few colours are required),
beginning on the right hand with white, yellow ochre, and so on, and going from the light to the
darker colours on the left.
It facilitates your work to have your colours arranged in a definite order.
The approximate quantities which you will ordinarily require are suggested by the proportionate sizes of the circles drawn on the diagram.