5f^' 



NATURE 



{April 2^, T878 



becomes of a milky aspect, so the oily and resinous substances 

 contained in paintings will become dim as soon as air penetrates 

 between their particles. The picture thus assumes a greyish, 

 dim appearance, and the pigments seem to have been fading. 

 That this is not really the case has been proved by the influence 

 of a process invented by Pettenkofer, which he calls regene- 

 ration. In a flat box the picture is exposed to air impregnated 

 with alcohol. Of this latter the resinous elements of the pic- 

 ture absorb a certain quantity, swell and fill up the interstices 

 between the separated particles so as to reunite them into an 

 optically homogeneous transparent substance. 



The alcohol does not affect in the same way the hardened oil. 

 If the interstices between its particles are not filled up by the 

 ftwelling resin, it becomes necessary to introduce a new substance 

 into the picture, and this is called nourishing a picture. 



Pettenkofer has the great merit of having clearly proved that 

 the nourishing of a picture with oils, as the custom was formerly, 

 and still is to some degree, is a very objectionable proceeding, 

 as it has the effect of darkening the colours for ever. He 

 recommends, instead of oil, balsam of copaiva, which has 

 become since an invaluable means for preserving and restoring 

 oil paintings, and will be more and more extensively used. 



I have frequently applied Pettenkofer's method, and with 

 very beneficial effect ; but whenever I mentioned it to profes- 

 sional picture-restorers, here as well as on the Continent, I 

 always found them to reject it, either ci priori, or after experi- 

 ments incorrectly made. 



In Munich, it seems, the pictures of all periods and of all 

 schools have had to suffer under local influences and through the 

 changes in the humidity of the air. This accounts for Petten- 

 kofer having principally described this, so to say, endemical 

 disease. In other galleries this affection does not appear so 

 frequently, and Pettenkofer's method, therefore, will not find 

 everywhere the same extensive application as at Munich. I 

 think, however, that with some modifications it may be employed 

 against some other alterations. I have, for instance, found it 

 efficacious with paintings which had been injured by exposure to 

 great heat. I shall show you a small picture which had been 

 hanging for a long time so near a gas flame that it was almost 

 completely scaling off, and so entirely faded that it scarcely 

 looked like an oil painting at all. In that state it was exposed 

 to alcoholised air, then nourished with balsam, and its back 

 slightly varnished ; and the scales starting from the canvas were 

 refixed by pressure. And now it appears fresh in colour, firm 

 in substance, and perfectly smooth on its surface. The old, 

 cracked varnish, melted together by the alcohol, looks as if fresh 

 laid on. 



Humidity sometimes favours the development of fungus. The 

 round, black, small spots which pass through the canvas and the 

 painting of these two pictures are produced by the same little 

 plant which Prof. Tyndall showed you when he spoke on the 

 highly interesting subject of spontaneous generation. 



Oil and water, so injurious to oil paintings, enter both into 

 the material used for lining. Anxious to exclude these sources 

 of danger, and to simplify the whole process, I have endeavoured 

 to replace it by a new method which I shall submit to you this 

 evening. 



How paintings may be disfigured by restorers you see in this 

 picture, which was renovated with oil colom-s according to the 

 practice only abandoned about thirty years ago, when it was 

 advantageously replaced by the use of varnish colours. 



The amount of external injury oil paintings sometimes endure 

 and stand is perfectly amazing. Pictures in the course of cen- 

 turies, during the destructive fury of wars and revolutions, may 

 have been torn out of their frames, rescued from below the niins 

 of burned monasteries, may subsequently have passed from one 

 l»ic-h-brac shop to another, where they have been piled up, to 

 be pulled about at each new inspection, and literally trodden 

 under foot, whereby they have finally been reduced to a state of 

 colourless, greyish, or black rags. Still such pictures may not 

 unfrequently be awakened, as it were, to new life, to their 

 original brilliancy of colour, if, with all necessary care, their 

 injured limbs are put together again, their wounds are healed, 

 and fresh nourishment, air, and thorough cleansing, are adminis- 

 tered to their lacerated bodies. 



A sound constitution is, of course, a necessary condition for 

 obtaining any such result, without it we can only obtain a partial 

 cure. We see this with reference to the Bolognal school of the 

 seventeenth century. The pictures which you see here are 

 instances of this. From the state of rags to which they were 



reduced they have passed, by appropriate treatment, into the 

 state of firm, even, well-conditioned, and clean pictures. The 

 constitutional alteration characteristic of their time and school, 

 however, could not be cured. You will, therefore, perceive that 

 the contrast is too great between light and shade, that the half 

 tones are too weak and that the glazings spread on dark ground, 

 which certainly existed formerly, have been destroyed by the 

 growing of bolus and umber of the priming. That this is not 

 the fault of the method of restoration is clearly proved by the 

 state in which you will find all the pictures of this school, even 

 those best preserved in the best galleries of all countries. 



The constitutional diseases of pictures belonging to the French 

 and to the English school of the last hundred years are of still 

 more serious nature, and much more difficult to cure. Many of 

 them, though they were never exposed to any injury whatever, 

 nor are likely ever to be so in our jDresent state of civilisation, 

 cannot be guarded from premature decay in spite of all possible 

 care with which they are kept. 



The principal symptoms of their bad constitution are : — 



1. Darkening of the opaque bright colours. 



2. Fading of the transparent brilliant colours. 



3. Darkening, and above all, cracking of the transparent dark 

 colours. 



The best opportunity to study these several appearances is 

 given us in the Museum of the Louvre, which contains a great 

 number of such pictures in the section occupied by the French 

 school. I have paid particular attention to the cracks in these 

 pictures, as I find that in shape, in size, in position, as well as 

 in relation to the various colours, they differ distinctly from the 

 cracks in older pictures and in those of other schools. This, of 

 course, is of importance, not only for the explanation of the 

 reasons which produced them, but as a symptom which, in a 

 given case, might determine the diagnosis, whether a picture be 

 an original or only a copy. The special characteristics of these 

 cracks are the following : — 



They are all but exclusively found in the thickly laid on trans- 

 parent dark colours, and they are the deeper and the more gaping 

 in proportion to the thickness of the layer of the colour and the 

 extent of the dark surface. The chief cracks run parallel to the 

 outlines of surfaces painted with bright opaque colours, such, for 

 instance, as are used for the flesh tints, and which are more or 

 less thickly laid on. But there is generally a slight distance 

 between the bright colours and the cracks. 



Lateral branches of these cracks pass into the white, but they 

 do not gape, provided the white colours had been laid on directly 

 upon the priming, and not upon a layer of dark transparent and 

 not sufficiently dried colour. 



This examination of the cracks of pictures has sometimes 

 afforded me a peculiar insight into the practice used for the 

 picture. In the well-known picture, for instance, by Gueri- 

 cault, of "The Wreck of the Medusa," in the Gallery of the 

 Louvre, the cracks follow exactly the outlines of the bright 

 flesh-tints. The arm of one of the dead bodies hanging in the 

 water is so covered by planks and water that nothing of the 

 forearm is to be seen. It is, however, very easy to prove that 

 originally that arm was painted in all its length, for the cracks 

 do not only follow the outline of the visible upper arm, but also 

 the no longer visible forearm, and all the five fingers. This 

 proves that the fore part of the arm and the hand were origin- 

 ally painted in flesh-tints before they were covered over by the 

 planks, and the water painted afterwards. In Ingres' portrait 

 of Cherubini, the face of the latter is beautifully preserved, 

 while that of the Muse, as well as her drapery, is covered with 

 cracks. In the depth of the cracks of the white drapery an 

 intense blue tint is to be seen. Mr. Henry Lehmann, of Paris, 

 the favourite pupil of Ingres, who knows the history of this 

 picture as an eye-witness, and whom I consulted about this very 

 striking appearance, gave me the following information : — 

 Ingres painted the head of Cherubini in Paris, and then took it 

 with him to Rome. There it was pieced into a new canvas and 

 lined. Then the Muse was painted, and before the colours were 

 perfectly dry, another model was chosen, and a new Muse 

 painted over the old one. The colour of the drapery was like- 

 wise altered, and this explains the cracks in the white colour, 

 and explains also why the blue appears in the depth of the 

 cracks of the drapery. 



Among the English artists of the last hundred years, some 

 have painted with the same material and by the same process as 

 their French contemporaries, and consequently with the same 

 unfortunate results. Others avoided these by using the same 



