We now come to the year 1494; but before dealing seriatim with the pictures painted at that time it will be well to refer briefly to a question of technique. Crowe and Cavalcaselle make a definite statement to which I can give no adherence. They speak of Pietro's work changing from tempera to oil work, and they allude to his inability at this time to use the new medium in all its complexity, and later on to his complete mastery over oil-painting and his constant use of it. Mr. Herbert Horne, on the other hand, states with an equal assurance that "all Perugino's pictures were painted in tempera on a gesso background,"[H] and I find it as difficult to accept this statement as that of Crowe and Cavalcaselle as a sufficient explanation of the question.
It is quite clear to a careful observer that the technique of the Albani picture differs from that of the triptych in the National Gallery, for example; but the difficulty is then only stated. It is an extremely puzzling question to determine from an old master painting whether it was painted in tempera or not. Even Ruskin once admitted that he had for a long time been holding up for admiration as the finest oil-painting what he finally discovered to be tempera. The repeated oiling and varnishing to which Italian pictures have been submitted renders the task of discriminating the original medium one of the greatest perplexity. When to this is added the further statement that in some pictures it would appear that the under-painting which gives the shadows is in tempera and the glazes in oil colour, the danger of making such dogmatic statements as those already mentioned, is still more apparent.
The information which we possess as to tempera painting in the fourteenth century is derived from the "Trattato" of Cennino Cennini, and this has just been re-translated by the one person in England, who, more than anyone else has practised and understands tempera work. Mrs. Herringham, who has for years worked in tempera and copied the Quatrocento pictures in the National Gallery, has discussed this abstruse question, and to her knowledge, derived both from personal conversation and from her invaluable book,[I] I have obtained much information, and have coupled it with close personal examination of the pictures, and some interesting experiments. I think, in considering tempera painting, one factor, that of climate, has not always received sufficient attention. Mr. Spencer Stanhope has expressed to Mrs. Herringham that tempera never dries completely in this country, and should not be varnished, but that has not been her experience. It, however, expresses in crude statement, the difficulty there is in this moist climate in using tempera satisfactorily, and there is little doubt that part of the success of Italian tempera work is due to the climate in which the artists worked. It is quite clear from Mrs. Herringham's work, that tempera painting, by which I mean strictly yolk-of-egg painting, is capable of the soft transparent effects which are to be seen in Perugino's pictures, and that no admixture of another vehicle with the egg is needful. It is not, however, clear whether the whole of many of his pictures were painted with yolk of egg alone.
I was in hopes at one time that a careful study of cracking and a comparison of the shape and formation of the cracks on different pictures would give me some definite formulæ by which the medium used could be detected, but a very careful examination only gave inadequate results. There appear to be certain thick ridge-like formations in the darker colours especially at the very edges of the draperies, which it is very difficult to imitate in tempera, and while the landscape is most clearly put in quite lightly in tempera, yet the draperies are so different in handling as to give the impression that another medium was used for them. There is also a curious variety in Perugino's pictures as to hatching, especially after 1500, and the hatching which till then only appears in the flesh, is later on to be seen in other parts of the picture. Blending of one colour with another is also to be seen in some of the later pictures to an extent that the earlier pictures never show, as with pure tempera painting the paint "cannot be moved and blended as in oil work," but "it must be put on and left alone till it is dry." I do not pretend to have touched more than the fringe of this subject, but my opinion is that Perugino did many of his pictures wholly in tempera, and that with others he used tempera for the under-painting and oil for the glazes, and that there are also pictures where size has been used as a medium for the draperies when great solidity and heavy cordy outline was desired. The question of oil colours cannot be dismissed in a sentence. Perugino probably learned a good deal as to the use of colours from the Gesuati, who were, as Vasari informs us, well practised in the art of colours, and conversant with glass-painting and enamel work, but the mystery remains as to how it is that the very fugitive colours he used have stood and remained as brilliant as ever.
For his Cantor Lectures in 1892,[J] Dr. A. P. Laurie carried out some remarkable experiments with certain fugitive colours and certain oils and balsams, with a view to ascertaining whether any oil varnishes were impervious to moisture, and securely locked up the colours against change. Some of these experiments I have repeated, and I have had some interesting conversation with Dr. Laurie, and I agree with him absolutely that the only vehicles which lock up the colours against moisture and against the action of sulphuretted hydrogen are those composed of balsams. The stickiness of colour ground in balsam to which he alludes can, I have ascertained, be overcome by a few drops of pure linseed oil and a morsel of wax, and the result can then be used easily with a brush. Experimenting with the balsams of the larch and of the silver fir, I have been able to protect verdigris, orpiment, and kermes lake securely, and the experiments have been mainly conducted with verdigris and orpiment as notoriously fugitive colours and yet colours which it is quite clear Perugino used.
It may be well perhaps to allude here to Vasari's story respecting the artist's use of ultramarine. The colour was so costly that in several of his contracts Perugino expressly stated that his patron was to provide it, and Vasari states that when he was painting in the cloister of the Ingesuati, the Prior, who himself prepared and supplied the ultramarine, was mean and mistrustful as to Perugino's use of it, and would always be present when it was used. The artist took the Prior's distrust to heart, and by constantly washing his brush in a bowl of water allowed more colour to be precipitated than he was using in his fresco. Having punished the Prior in this way, he gathered up the blue from the water and returned it to him with the words, "This belongs to you, father; Learn to trust honest men, for such never deceive those who confide in them, although they well know how to circumvent distrustful persons like yourself when they desire to do so." Pliny records a singular story about vermilion. Perugino's skies were painted with this colour, and put on very thinly, and they have a peculiar formation of cracking which is quite recognisable.
As regards grounds, I believe that all Perugino's panel pictures are upon gesso laid upon panel, but in many of them it seems to me that linen has been used between the panel and the gesso as if to bind them together. Verdigris is, I believe, the only colour that will produce some of Perugino's greens, and, as far as I have experimented, the balsams, as Venice turpentine and olio d' abezzo, are the only varnishes that protect it unchanged against the action of sulphuretted hydrogen and moisture.
These few statements as to technique are only suggestive. I am not a chemist, and the subject demands prolonged experiments in a laboratory; and such experiments should result in most interesting discoveries. Resta calls Perugino's colouring dry and sparing; Lanzi alludes to what he terms its skimpiness, but the very thinness of it is but proof of the artist's complete mastery of his medium, and that this medium was always mainly tempera, and was never what we know as oil painting is my distinct opinion, based upon an examination of almost every one of his works in Italy.