§ 81. The Fresco Process.

Of all the methods that painters employ, painting on the wall is the most masterly and beautiful, because it consists in doing in a single day that which, in the other methods, may be retouched day after day, over the work already done. Fresco was much used among the ancients, and the older masters among the moderns have continued to employ it. It is worked on the plaster while it is fresh and must not be left till the day’s portion is finished. The reason is that if there be any delay in painting, the plaster forms a certain slight crust whether from heat or cold or currents of air or frost whereby the whole work is stained and grows mouldy. To prevent this the wall that is to be painted must be kept continually moist; and the colours employed thereon must all be of earths and not metallic and the white of calcined travertine [Sangiovanni white]. There is needed also a hand that is dexterous, resolute and rapid, but most of all a sound and perfect judgement ; because while the wall is wet the colours show up in one fashion, and afterwards when dry they are no longer the same. Therefore in these works done in fresco it is necessary that the judgement of the painter should play a more important part than his drawing, and that he should have for his guide the very greatest experience, it being supremely difficult to bring fresco work to perfection. Many of our artists excel in the other kinds of work, that is, in oil or in tempera, but in this do not succeed, fresco being truly the most manly, most certain, most resolute and durable of all the other methods, and as time goes on it continually acquires infinitely more beauty and harmony than do the others. Exposed to the air fresco throws off all impurities, water does not penetrate it, and it resists anything that would injure it. But beware of having to retouch it with colours that contain size prepared from parchment, or the yolk of egg, or gum or tragacanth, as many painters do, for besides preventing the wall from showing up the work in all clearness, the colours become clouded by that retouching and in a short time turn black. Therefore let those who desire to work on the wall work boldly in fresco and not retouch in the dry, because, besides being a very poor thing in itself, it renders the life of the pictures short, as has been said in another place. 

CHAPTER VIII. (XXII.)
Of Painting in Oil on a Wall Which is Dry.

§ 86. Mural Painting in Oil.

When artists wish to work in oil on the dry wall two methods may be followed : first, if the wall have been whitened, either ‘a fresco’ or otherwise, it must be scraped; or if it be left smooth without whitening but only plastered there must be given to it two or three coats of boiled oil, the process being repeated till the wall cannot drink in more, and when dry it is covered over with the composition or priming spoken of in the last chapter. [§ 84. How to Prime the Panel or Canvas. I must now explain how to set about the work. When the artist wishes to begin, that is, after he has laid the gesso on the panels or framed canvases and smoothed it, he spreads over this with a sponge four or five coats of the smoothest size, and proceeds to grind the colours with walnut or linseed oil, though walnut oil is better because it yellows less with time. When they are ground with these oils, which is their tempera (medium), nothing else is needed so far as the colours are concerned, but to lay them on with a brush. But first there must be made a composition of pigments which possess seccative qualities as white lead, dryers, and earth such as is used for bells [terra di campagna, bell black] all thoroughly well mixed together and of one tint, and when the size is dry this must be plastered over the panel and beaten with the palm of the hand, so that it becomes evenly united and spread all over, and this many call the ‘imprimatura’ (priming).] When this is finished and dry, the artist can trace or draw on it and can finish such work in the same manner as he treats the panel, always having a little varnish mixed with the colours, because if he does this he need not varnish it afterwards. The other method is for the artist to make, either with stucco of marble dust or finely pounded brick, a rough cast that must be smoothed, and to score it with the edge of a trowel, in order that the wall may be left seamed. Afterwards he puts on a coat of linseed oil, and then mixes in a bowl some Greek pitch and resin (mastice) and thick varnish, and when this is boiled it is thrown on to the wall with a big brush, and then spread all over with a builder’s trowel that has been heated in the fire. This mixture fills up the scores in the rough cast and makes a very smooth skin over the wall, when dry it is covered with priming, or a composition worked in the manner usually adopted for oil, as we have already explained.

From, Vasari on Technique, Translated from the Italian by Louisa S. Maclehose, London: J. M. Dent & Company, 1907. Reprinted by Dover Publications, Mineola, N. Y. 1960, 221-2, 230-1, 233.

Giovanni Battista Armenini of Faenza

On the True Precepts of the Art of Painting / De Veri Precetti della Pittura
Ravenna, 1586

from Book 2 Chapter VII

Of the distinctions and kinds of pigments and of their particular natures; how they are prepared differently to achieve better effects in paintings; with which and how much liquid they are used; in what way mixtures are made to find any tint, especially for flesh in all its varieties and in accordance with the natural complexion of people, and how these tints ought to appear in the end; of the three principal ways of painting with pigments, the first of which shall be work in fresco.

I assume that every ordinary painter knows that the colours [pigments] used in painting are of two kinds, namely, the natural, or to use another name, mineral, and the artificial. In order to work with these, one generally dilutes them with three liquids: water, glue, or oil. The first method is called work a fresco, the second, a secco, and the third, oil. First, as is known, artificial pigments never work well in fresco, and there is no way of making them endure, especially in the open, because they require very dry surfaces and dry places; but we will deal with the qualities of each type of pigment more closely in the proper place. Now you must know that grounds made of one tone or colours are mixed in various ways, some being made lighter and some darker; one creates many tints from only one pigment through the incorporation of white and black. But finally, all art deriving from the artist, the errors thus born of the artist are caused either by badly mixed and poorly compounded pigments or by an uncertain hand, ill-practiced in the arranging and harmonising of colours, which should be pure, vivid, and harmonious. Thus, I have always urged students to work at and continually practice the use of colours in order to learn their effects so that they will then be able to use pigments with sureness and perfection. Just as the principal intent of the poet is to delight by diversifying his poem with various colourations, the same effect must be sought by the painter with diverse and beautiful colours. Even though the storia and inventions may be delightful in themselves because of the subject, if the colouration, which is the means of explaining the inventions, is not agreeable to the eyes of the beholder, one will never be able to produce the effect that the poet does. From united and harmonious colours that beauty is brought forth which enraptures the eyes of the ignorant and stealthily enters the minds of the wise. One sees that true resemblance is born of proper tints, and the more vivid the tints, the more they enrapture and please, especially lords, most of whom make use of paintings to embellish their palaces; for lords are moved more by the delight and pleasure they take in the variety and charm of the colours than by works admired for their excellence of design. Thus, they follow more the dictates of the eye than of the mind. A beautiful variety of harmonious colours conveys to the eye that which harmonious music usually brings to the ear when low notes meet the high pitched, and the middle notes resound in harmony; from such diversity, a resonance and an almost marvellous union of measures is achieved, the soul is transfixed in wonder.

     But the sum of the science of colouration revolves about this: From various kinds of mixed and pure pigments, composed with order, is born a well-planned and united composition, which in no way is discordant. A harmonious composition is neither so gaudy that it looks like a coloured tapestry, nor is it so sombre that the true tints of flesh or nearby objects cannot be discerned. Therefore, the perfect way will be that which lies between the garish and the murky. The pigment colours and the mixtures must be genuine and true, with a soft and delicate union that resembles a pure and shining beauty. We shall not relate in detail the materials of pigments, nor give their kinds and qualities, since these are known to all. But it is well to speak of some of their particular properties and warn of certain effects caused by the fact that some of these properties are contrary to each other, which presents serious problems.

     It is well, then, that each pigment we acquire be the most beautiful, pure, and genuine of its type as possible. Then we must be careful in using them so that they remain pure and distinct, for if the slightest amount of another mixture touches them, usually in the form of dust, they become muddy and lose a great part of their purity and brightness. In using pigments, one must be both practiced and diligent. But in using pigments a fresco, keep in mind that, as has been said, the wall desires only natural pigments born from the earth, for there are different types of earth, each with its own colour. I believe that these are commonly known throughout Italy. Natural pigments are ground finely with pure water, except smalto and other similar blues. For the white used in fresco, as one knows, one takes the best of the whitest lime [San Giovanni white], usually that found in Genoa, Milan and Ravenna. But before the lime is used, it must be cleansed well, as is done by painters in several ways. Some first boil the lime on a very hot fire, keeping the foam high. This is done to remove the brine and to diminish its power of crystallizing when the lime later dries on the wall. Once the boiled lime has been cooled in the air and the water removed, it is placed in the sun on newly baked bricks; when it has dried, the lighter it is, the better it has been cleansed. There are painters who bury the lime after they have cleansed it in this manner and keep it buried for many years before they use it. Others keep it on the roofs of houses in the open air. Some compound it with half again as much finely ground marble. It has been seen that the lime can also be cleansed by putting it in a large vase in the open air, adding boiled water, and stirring the mixture with a stick. The next day it is placed in the sun. This method cleanses the lime sufficiently to permit its use in grounds the next day, but not in painting nudes, for they would not last intact without deterioration.

     Pigments prepared and settled in the prescribed way are placed in pots so they can be preserved unadulterated. Then one takes crocks or other vessels and begins to make mixtures by first placing some of the white in three or four crocks, and black in as many others, but not as much back as white. Then one takes the pots of pure pigment, either yellow, bright red, blue, green, or whatever one wants, and puts some of the pigment with the white in the crocks, so that at least three mixtures are made, one lighter than the next, according to the amount of pure pigment mixed with the white. One then repeats the process by mixing the same colour with black and another dark shade, observing the preceding instructions in order to make one mixture darker than the next. Through this procedure, each pure pigment yields four or six or as many mixtures as one wants, as found in drawings or well-executed cartoons. We shall not discuss the diversity of colours which nature exhibits in the most minute gradations. Their number is very great, as one can imagine if one considers just fruits and flowers, which are so plentiful in their variations. And it is through the mixing we have described that the true tints of each are made.

From, Giovanni Battista Armenini, On the True Precepts of the Art of Painting, Translated from the Italian by Edward J. Olszewski. Burt Franklin & Co., 1977.