The Practice of
Tempera Painting - Artificial Emulsions

Unlimited Possibilities
I have referred briefly here and there to other sorts of tempera and other kinds of handling. Some of the most useful and agreeable of these techniques depend upon the use of artificial emulsions. Egg yolk is a natural emulsion, a mixture of watery and oily parts. Artificial emulsions may be made in innumerable combinations, many of which have strikingly individual working characters as painting media. Some are good, some bad, technically considered. Some are strong and permanent; others are not. Some contain soaps and other objectionable ingredients; others are stably compounded out of innocuous and mutually compatible materials. Only the most cursory reference to these media can be given here. [p. 128]

A Basic Formula
Certain substances act as emulsifying media. Oily materials can be added to them, and then watery materials, and the oil and water will not separate, but remain for some time in intimate mixture. The most important bases for artificial emulsions are egg yolk, casein solutions, and glue. These form genuine emulsions with oils and varnishes, which may be used for serious painting. So-called emulsions made with gum water are to be avoided. An emulsion may be made from pure egg yolk and oil or varnish by mixing thoroughly one volume of the yolk with an equal volume of the oil or varnish, and adding gradually two volumes of water. This is a sort of basic formula.

The oil used may be raw or boiled linseed oil, or stand oil, or China wood oil [which gives a washable surface], or strong mastic varnish, or any of many mixtures of these and other things. Balsams such a Venice turpentine are sometimes used, but their effect is of doubtful quality. Beeswax dissolved in turpentine may be used in [p. 129] place of the oil, or mixed with it; and this sort of emulsion is especially useful for such delicate work as flower painting. [pp. 129-130]

Casein Emulsions
In place of the egg yolk in this basic formula, a solution of casein may be used. Casein is often dissolved in strong ammonia; but a better solution is obtained, and that more easily , by warming one ounce of dry powdered casein in sixteen ounces of water, and adding gradually one half ounce of powdered ammonium carbonate. After the foam subsides, a thick, honey-like solution is left, and this may be used as an emulsifying agent. It produces emulsions which load more than those made with egg, and are more crisp working and "short." Casein, in the form of washed cheese, dissolved by grinding with slaked lime to a thick paste, gives an admirable medium for wall painting if you add a small amount of strong hide glue [one part in ten of one-to-ten glue solution] and thin the mixture with warm skimmed milk. With this composition it is possible to produce effects indistinguishable from those of fresco. The surface is washable [within reason] when it is dry. [p. 130]

Underpainting for Oil
Any good tempera may be used as an underpainting for oil; and some [especially the egg temperas] lend themselves also to painting over oil, especially to rendering fine or sharp detail over or under a glaze of oil paint. The technical problems and possibilities that these techniques open up lie far beyond the scope of this introduction. Stand oil, or boiled linseed oil, or copal varnish, or combinations of these, may be emulsified with an equal part of a thick, warm solution of glue, and two parts of water added. This sort of emulsion is particularly agreeable for broad underpaintings for oil, and can readily be made to yield certain technical effects, such as are seen in the works of Tintoretto and El Greco. [p. 130]

Preparation of Wall Surfaces
All these combinations have their proper places, but they cannot be discussed in detail here. In general, they resemble the tempera [p. 131] that we have been considering in working properties, but differ from it in their specific characters. They are more suitable than plain egg for working on a large scale. Admirable decoration can be carried out directly on a wall, or on a wall lined with muslin or paper, or both, with emulsions of this sort. The colors may be mixed with the emulsion to the consistency of house paint, and applied with bristle brushes, thinning with water as required. If possible, most modern walls should be lined with muslin, or better, with linen, glued on in pieces [after the wall is sized] with hot glue. Kraft paper may be hung over this with paste, or applied directly to the sized wall. An even tint may be given to the linen or paper by applying two or three coats of tempered color, or of a mixture of 16 ounces of whiting with 16 ounces of one-to-twenty-four glue solutions, with or without the addition of a little coloring matter, such as ocher, red earth, black, or French ultramarine.

I can do no more here than indicate the existence of these means, and say that, in my opinion, they can best be utilized by persons who have already learned the fundamentals of tempera painting as distinguished from all other media, by the practice of the most rigorous of all tempera disciplines, that of pure egg painting. The practice that I have attempted to set forth should be regarded as an introduction to the character of tempera in general. For a given painter, with a given job to do, there is some one technique more suitable than any other. In some cases, these will be a tempera of some sort; and in a few of those, the tempera described at some length in this book. This method will, I believe, equip a painter with the experience necessary to test and understand and use effectively other methods, barely mentioned here, which he may then find better fitted to his needs. [pp. 130-131]