494 



NATURE 



{April iS, 1878 



priming, and to dry quicker, and moreover, of containing a white 

 absolutely innocuous to the others. 



The inconveniences, on the other hand, are : that it more 

 easily breaks, and under the influence of humidity separates 

 from the canvas. 



2. The oil priming consists of several coats of oil colours. 

 As each of these must be perfectly dry before the next is laid 

 on, and as, moreover, time must be given to the whole to 

 dry completely before painting upon, in order to avoid the 

 sinking in of the colours, the whole preparation is much 

 slower than the distemper. Nevertheless it is now generally 

 adopted. 



Rey, in France, has pointed out a process which is a compro- 

 mise between the two methods ; he begins by distempering, and 

 after several coats of distemper, having dried one after the 

 other, he puts a coat of oil which, as it were, changes the dis- 

 tempered ground into an oil-colour ground. 



With oil priming it is of importance that the principal colour 

 be white-lead, to which are added comparatively small quantities 

 of yellow, black, or other colours. For a whole century a 

 school, that of Bologna, predominated in Italy, which aban- 

 doned this principle. During the second half of the seven- 

 teenth and the first half of the eighteenth century, most of the 

 Italian masters of other schools followed its example. Probably 

 for the purpose of obtaining more easily the desired effect of 

 the chiaroscuro, they painted on a brownish-red priming, which 

 consisted of bolus mixed with umber. Not one of those pic- 

 tures has kept its original colouring. tNot only has the priming 

 caused all the dark parts to gi-ow much darker, but it has 

 destroyed, or nearly so, all the glazing, so that only those 

 colours can be recognised which either contain white, or are 

 glazed on white. I can show you numerous instances of this, 

 for, on account of the extreme fertility of this school, there is 

 little difficulty in procuring pictures of masters of that time or 

 of their pupils. 



Wood priming does not require the same elasticity as that of 

 the canvas, which ought to be capable of being rolled. There- 

 fore the priming of the wood shows less variations. It is gene- 

 rally composed of chalk or plaster, tempered with starch, paste, - 

 size, or glue, and more or less thickly laid on. In some pictures 

 of different centuries we find, either between the wood and the 

 priming, or between the priming and the painting, canvas, and, 

 exceptionally, even paper. 



The diseases of the priming are not of a very complicated 

 nature. They manifest themselves principally in three different 

 ways : — i. By cracks in the priming itself. 2. By the sever- 

 ance of the priming from the painting. 3. By the severance of 

 the priming from the wood or the canvas. The third disease is 

 by far the most frequent, especially among pictures on canvas 

 distempered with paste. If small pieces only are scaling off or 

 blistering, they are fixed again to the ground by letting a sohi- 

 tion of size pass between the detached part and the^ canvas, and 

 pressing both gently together. If the deterioration extends 

 over a considerable surface, the picture has to be lined. While 

 this is being done, and while the gluing substance penetrates 

 into the picture, the detached parts are pressed on again with 

 slightly heated irons. If the whole priming threatens to come 

 off, it will be better to take the picture entirely from the panel 

 or canvas, and to transfer it to a new canvas. 



I shall show you examples illustrating the before-mentioned 

 points, and among them two pictures ; one in oil, taken off 

 from canvas, the other in tempera, taken off from wood. Both 

 of them, strange to say, have escaped destruction without 

 having been transferred to a new canvas, and without being 

 covered with paper, as is usually done, before taking them off. 

 They show you the painting by itself from both sides. I have, 

 of course, used every precaution in bringing them safely over 

 from P'lorence, where I happened to discover them carelessly 

 stowed away among heaps of old pictures. 



We come now to the most important part of the picture, the 

 painting itself. We meet very often with the idea that the old 

 masters had been in possession of colours, that is pigments, the 

 knowledge of which has been lost, and that this accoimts princi- 

 pally for the difference between the oil painting of the fifteenth 

 and sixteenth centuries, on the one hand, and that of the 

 eighteenth and nineteenth on the other. But this is a great 

 mistake. We know perfectly well the pigments used by the old 

 masters ; we possess the same, and a considerable mimber of 

 new ones, good as well as bad, in addition. In using the ex- 

 pres;;ion of good and bad I am principally thinkii^g of their dura- 



bility. From this point of view the pigments can be placed 

 under three headings : — 



1. Those which are durable in themselves, and also agree 

 well with the other pigments with which they have to be mixed, 



2. Such as when sufficiently isolated remain unaltered ; but 

 when in contact with certain other pigments change colour, or 

 alter the others, or produce a reciprocal modification. 



3. Those which are so little durable that, even when isolated 

 from other pigments, the mere contact of the vehicle, the air, or 

 the li^ht, makes them in time fade, darken, or disappear alto- 

 gether. 



The old masters used, without reserve, only those belonging 

 to the first of these categories. For those belonging to the 

 second they imposed on themselves certain limits and precautions. 

 Those belonging to the third they did not use at all. 



That some of the modern masters have not followed these 

 principles is not owing to a lost secret, but to the fact that they 

 disregarded those well-known principles, and even consciously 

 acted against them. In Sir Joshua Reynolds's diary, for instance, 

 we read that in order to produce certain tints of flesh, he mixed 

 orpiment, cannine-lake, and blue-black altogether. Now orpi- 

 ment is one of the colours of the second category, carmine-lake 

 one of the third. That is to say : orpiment, as long as it remains 

 isolated, keeps its brilliant yellow or reddish-orange colour ; but 

 when mixed with white-lead it decomposes, because it consists 

 of sulphur and arsenic, and it, moreover, blackens the white- 

 lead, because the sulphur combines with it. Carmine-lake, even 

 if left isolated, does not stand as an oil colour, and therefore 

 has been superseded by madder-lake. 



Unfortunately some of the most brilliant colours are perish- 

 able to such a degree that they ought never to be used ; yet, it 

 seems to me, that just in one bi-anch of art in which of late 

 remarkable progress has been made, I mean landscape painting, 

 the artists, in order to obtain certain effects of colour not easily 

 to be realised, do not always resist the temptation to make use 

 of a number of pigments, the non-durability of which is proved 

 beyond doubt. However that may be, I think it pretty certain 

 that the pigments in themselves play only a subordinate part in 

 the deterioration of oil paintings, and that the principal part 

 belongs to the vehicle with which the colours are ground, and to 

 the liquids which are added during the painting. I hope, there- 

 fore, you will excuse my making some ■ elementary exi^lanations 

 about these liquids. 



Oil and fat are bodies consisting of carbon, hydrogen, and 

 oxygen. They may be considered as salts in which glycerine, 

 as a basis, is combined with different acids, stearic acid, palmic 

 acid, oleic acid. If oil is exposed to the air it changes ; certain 

 kinds of oil remain liquid ; others become thicker and darker, 

 and are gradually transformed into hard and opaque bodies. The 

 drying of oils is based upon a chemical process, during whicli 

 the oil oxidises by absorbing oxygen from the air, and combining 

 a part of it with carbon to form carbonic acid, and another part 

 with hydrogen to form water. The different oils dry with dif- 

 ferent rapidity, but this rapidity may be modified by the presence 

 of certain substances, or by certain treatment. Tinseed oil, for 

 instance, according to the way in which it has been pressed out 

 of the seed, contains more or less mucilaginous substances. 

 These latter impede the drying of the oil, and have therefore to 

 be removed by a refining process. If linseed oil in a shallow 

 vessel is exposed to the air and light, and especially to a green 

 light, it soon begins to dry, and is transformed first into a kind 

 of varnish and gradually into a solid opaque substance. The 

 drying may he quickened by boiling, and more particularly by 

 the addition of lead, zinc, or manganese. In this way a quick- 

 drying oil varnish may be prepared and used as a siccative. It 

 follows that there are certain substances which impede the drying 

 of oils, and others which facilitate it. Amongst the pigments 

 are some which belong to this category of bodies ; white-lead, 

 zinc-white, minium, vermilion, for instance, facilitate the 

 drying ; others, such as ivory-black, bitumen, madder-lake, will 

 impede it. Supposing, now, we should add to each of the 

 different pigments the same quantity of oil, the drying of it 

 would progress at different rates. But in reality this difference 

 is very greatly increased by the fact that the different pigments 

 require very different quantities of oil, in order to be ground to 

 the consistency requisite for painting. 



Pettenkofer quotes the following figures, given to him by one 

 of the colour manufacturers : — 



100 parts (weight) White-lead require 12 parts of oil. 



,, ,, Zinc-white ,, 14 ,j 



