Vasari on technique

by Giorgio Vasari

[§ 81, The Fresco Process, ante, p. [221].]

The fresco process is generally regarded as one of several methods for the production of pictures. It is better to consider it in the first place as a colour finish to plaster work. What it produces is a coloured surface of a certain quality of texture and a high degree of permanence, and it is a secondary matter that this coloured surface may be so diversified as to become a picture.

The history of the process is involved in obscurity, and it is not known who first observed the fact that colours mixed only with water when laid on a wet surface of lime plaster dried with the plaster and remained permanently attached to it. The technique was however known to the Romans, and we obtain the best idea of its essential character from the notice of it by Vitruvius in the third chapter of his seventh book. It is there treated in intimate connection with plaster work, as only the last stage in the technical treatment of a wall. The wall is constructed of stone or brick; it is then plastered; and the plaster is, or can be, finally finished with a wash of colour. Of the character of this antique plaster work something has already been said in a note to § 72, in connection with Sculpture (ante, p. [171]). It could be finished either in a plain face of exquisite surface that might even be polished, or with stamped ornaments in relief or figures modelled by hand; but it could also be completed with colour in the form either of a plain tint or a picture, and this colour would be applied by the fresco process.

Painting ‘a fresco’ means painting on the freshly laid and still wet final coat of plaster. The pigments are mixed with nothing but pure water, and the palette of the artist is limited by the fact that practically speaking only the earth colours, such as the ochres, can be used with safety; even the white has to be made from lime—the Italians called it ‘bianco San Giovanni’—as lead white, called ‘biacca,’ is inadmissible. Vegetable and metallic pigments are as a rule excluded from use. The reason why pigments mixed with water only, without any gum or similar binding material, adhere when dry to the plaster is a chemical one. The explanation of it was given by Otto Dönner in an Appendix to Helbig’s Campanische Wandgemälde, Leipzig, 1868, and is to be found also in Professor Church’s Chemistry of Paints and Painting. When limestone is burnt into lime all the carbonic acid is driven out of it. The result of the slaking of the lime by water, which is preliminary to its use in plastering, is that the material becomes saturated with an aqueous solution of hydrate of lime. This hydrate of lime rises to the surface of the plaster, and when the pigment is laid on, to use Professor Church’s phrasing, it ‘diffuses into the paint, soaks it through and through, and gradually takes up carbonic acid from the air, thus producing carbonate of lime, which acts as the binding material.’ To put the matter in simpler language, lime when burnt loses its carbonic acid, but gradually recovers it from the air, and incidentally this carbonic acid, as it is re-absorbed, serves to fix the colours used in the fresco process. It is a mistake to speak of the pigment ‘sinking into the wet plaster.’ It remains on the surface, but it is fixed there in a sort of crystalline skin of carbonate of lime which has formed on the surface of the plaster. This crystalline skin gives a certain metallic lustre to the surface of a fresco painting, and is sufficient to protect the colours from the action of external moisture, though on the other hand there are many causes chemical and physical that may contribute to their decay. If however proper care have been taken throughout, and atmospheric conditions remain favourable, the fresco painting is quite permanent.

The process of painting, it will be easily seen, must be a rapid one, for it must be completed before the plaster has time to dry, which it would do if left for a night. Hence only a certain portion of the work in hand is undertaken on each day and only so much of the final coat of plaster, called by the Italians ‘intonaco,’ is laid by the plasterer as will correspond to the amount the artist expects to cover before nightfall. At the end of the day’s work, the plaster not painted on is cut away round the outline of the work actually finished, and the next morning a fresh patch is laid on and joined up as neatly as possible to that of yesterday. In the making of these joints the ancient plasterer seems to have been more expert than the Italians of the Renaissance, and the seams are often pretty apparent in frescoes of the fifteenth and sixteenth centuries, so that they can be discerned in a good photograph. When they can be followed, they furnish information, which it is often interesting to possess, as to the amount that has been executed in a single day.

To prevent loss of time it is necessary to have a full-sized cartoon in readiness so that the drawing can be at once transferred to the coat of wet plaster as soon as it has been laid. Vasari speaks of these cartoons in § 77, in the second chapter on Painting, ante, p. [213]. The use of the iron stylus for impressing the lines of the drawing on the wet plaster is to be traced in some of the later Italian frescoes. Another process for carrying out the transfer was called ‘pouncing.’ For this the lines of the cartoon were pricked and dabbed with a muslin bag filled with powdered black, so as to show in dotted contours upon the wall.

Vasari is eloquent, both here and in a passage in his ‘Proemio’ to his whole work, on the judgement, skill, and decision necessary to paint successfully in fresco under these conditions and within these limits of time. The ideal of the process was to complete each portion absolutely at the one sitting. When the wall is once dry, any retouching, reinforcement of shadows, and the like, must be done ‘a secco,’ ‘on the dry,’ that is with pigments mixed with size, egg, or some other tempera, which will bind them to the surface. These after-touches lack the quality of texture and permanence of the true fresco (buon fresco). If size or gum have been used, they can be washed off the wall, and having been laid on a dry surface by a kind of hatching process they are harsh and ‘liney.’ It is often possible in good large-scale photographs to distinguish between the broad soft touches of the frescoist laid on while the ground was wet, and the hard dry hatchings of the subsequent retouching.

The illustration, Plate XV, has been chosen as a good example of the fresco technique. It shows the head of Mary from Luini’s fresco of the ‘Marriage of the Virgin’ at Saronno. The painting is executed in a broad and facile manner, the tints and tones which give the colour and the modelling being deftly fused while the whole is wet, and the darker details, such as the locks of the hair, are struck over the moist ground so that the touches seem soft and have no appearance of hatching. The light-coloured leaves of the garland round the head show the same softness, and they are laid in with a full brush in thick pigment. On the other hand there are marks of retouching where the shadows round the eyes, the corner of the mouth, etc., have been reinforced ‘a secco,’ perhaps by a restorer. These show as thin, hard, wiry lines, and have quite a different appearance from the work on the wet plaster.

It was only in the palmy days of Italian painting, from the latter part of the fifteenth century onwards, that artists were able to dispense almost entirely with retouching. In the earlier period of Giotto and his successors much more was left to be done ‘a secco,’ but the Giottesques fully understood the importance of doing all they could on the wet plaster, and Cennini in the 67th chapter of his Trattato insists that ‘to paint on the fresh, that is a fixed portion on each day, is the best and most permanent way of laying on the colour, and the pleasantest method of painting.’ The truth is that the technique of ‘buon fresco,’ while apparently understood by the Romans, was lost in the west during the early middle ages, though it may have been maintained in the Byzantine cloisters. In the course of the progressive improvements in the art of painting in the fourteenth and fifteenth centuries the old technique was gradually recovered. Recently Ernst Berger, in his Beiträge zur Entwicklungs-Geschichte der Maltechnik, I and II, München, 2nd ed., 1904, has denied that the Romans used the fresco technique, and has evolved an ingenious theory of a derivation of fresco painting from the mural work in mosaic which flourished in the Early Christian centuries. See note, ante, p. [255]. Into the question thus raised it is not necessary to enter, because no reader of Vitruvius or Pliny can have the shadow of a doubt that they knew and were referring to the fresco process. The words of Vitruvius (VII, iii) ‘Colores autem, udo tectorio cum diligenter sunt inducti, ideo non remittunt sed sunt perpetuo permanentes, quod calx,’ etc., and those of Pliny (XXXV, 49) ‘udo inlini recusant’ employed of certain colours which are known not to be admissible in fresco are quite conclusive on this point, and it does not advance science to build up elaborate theories on a denial of obvious facts.