If yet another comparison with music may be made, this technique corresponds somewhat to the final and most polished of interpretations, perhaps of a piano sonata, played by an artist who has long since committed the sequence of notes to ear and finger and can apply himself more to tempo and touch.
This mixed technique is the one used by the true master of his craft; it belongs to work in the studio based on thorough and constructive thought, where the very slightest potentiality of the paint can be used to its maximum. Every single operation can be broken down to the smallest detail. If you wish to sustain your attempt and achieve its object, you must be clear in your aims, in command of your medium, and skillful in execution. You cannot hope to work as you would with the alia prima technique, developing color effects of formal designs from a vague idea while you are painting.
Mixed techniques are built up in the following way: on a carefully prepared white glue ground, make a rough sketch in red chalk. Next, go over the firm outlines in watercolor. At this stage, considerable detail may be included, since the drawing will not receive a thick coat at the beginning; subsequently, however, every part of it will be used.
For tinting, use a 1:3 mastic solution, or a light balsam solution with the addition of the pigment powder, possibly terre verte, to give a nice spreadable glaze. If the ground is too absorbent, it needs a preliminary coat of shellac as insulation.
This glaze is also known as the imprimatura. This concept is derived from a method of chalk drawing used by Holbein the Younger (already mentioned in the section on drawing). In tracing from life, a little of the red chalk was pressed from the back of the tracing paper onto the new sheet of paper, leaving a faint red outline.
The idea of "imprimatura," then, comes from the "impression" made by the tracing chalk. Here the purpose is very much the same as that of the imprimatura in drawing, but achieved with the brush; it gives a monochrome underlying tone on which to obtain a moulded effect by lightening with white. This means that using white lean tempera directly on the imprimatura while still wet, you now paint in your brighter tints over a line or color drawing, so that the drawing shows through. Thus, the picture begins to take shape as a tone monochrome chalk drawing.
This lightening with white should allow the color of the imprimatura to show through even where it is brightest, and should go lightly over the darker parts of the picture, so that in the end the entire imprimatura receives a coat of lean tempera.
A notable characteristic of this method is that the resinous solution takes up the watery tempera so well - tackily, it must be admitted, but with great power of absorption. The two layers dry out rapidly, at least superficially, and are quite hard and free from tackiness within a few hours.
A second characteristic, and one which becomes clear only when the whole process is repeated, is that when using lean tempera direct on the wet imprimatura you can draw lines finer than any you could achieve with oil paint, for example. The old masters portrayed the delicate lines of beards and furs and chased work in jewelry in this way, using marten-hair brushes.
When all the paint has dried and no sticky patches are left, a second imprimatura should be laid on. This time, concentrated essence can be used for mixing; furthermore, the different parts of the picture can now be colored in in their appropriate local color. Here you will see why the first imprimatura had to be entirely covered with tempera; the tempera protects the second imprimatura from possible running and smudging.
In the areas of wet local color you should next lay either lean tempera (white) alone, or paint with all the colors in your palette (this is far from the final layer in your picture) in a very unobtrusive hue, at first an intimation of what is to come. At this stage your picture will correspond somewhat to the rapid sketch, well-diluted in turpentine, which serves as the underpainting in alia prima oils.
If in the course of the second application of tempera the imprimatura dries off somewhat, you may continue to paint over it. If the watery tempera colors run, however, you must again apply resinous varnish. The expert way would be to paint the whole picture in this manner; in other words, continue painting further coats onto resinous glazes.
On the principle of fat on lean, you will use fatty tempera in the upper layers, particularly when you wish to paint direct onto a layer of tempera without a resinous glaze when you complete the picture. It is not so usual to lay a final coat of over-fatty tempera as it is to varnish the whole picture over when it is completely dry, using a waxy mastic essence or wax alone.
This imparts a smooth, hard enamel-like surface to the picture. There is no sense in using impasto painting in mixed technique, which in any case is unsuited to the artistic concept involved. This is a technique which extracts the utmost from binding agents and pigments, or, to put it differently, which entails no waste of material.