April i^, 1878] 



NATURE 



493 



source of supply of a substance fully as efficacious as, or perhaps 

 more so than, atropine or belladonna, has for some time past 

 attracted much attention in the colony where the plant grows, 

 and has quite recently been brought to the notice of the Pharma- 

 ceutical Society. It is perhaps worth noting, that one of the 

 colonial names of Diiboisia myoporouies is the cork wood 

 tree, so named from its light brown corky bark. The wood is 

 of a light yellow colour, even grained, but soft, and used in the 

 colony for carving. Specimens of the wood are contained in the 

 Kew Museum. 



Thk additions to the Zoological Society's Gardens during the 

 past week include an Arabian Baboon {Cynocephalus hama- 

 dryas) from Arabia, presented by Dr. A. P. Woodforde ; two 

 Chacma Baboons {Cynocephalus porcarms) from South Africa, 

 presented by Capt. W, L. Coke ; a Green Monkey {Cercopithccus 

 caUilrichus) from West Africa, presented by Mr. Milward ; a 

 Great Kangaroo (Macropus giganteus), a Laughing Kingfisher 

 (Dacelo gigantea) from Australia, presented by Lieut. Crawford 

 Cafiin, R.N. ; a Short-eared Ov/\ [Ottts bmchyolus), European, 

 presented by Mr. W. K. Stanley ; a Golden-winged Parrakeet 

 (Brofogetys chrysopterd) from the Amazons, received in exchange ; 

 a South American Rat Snake {Spilotes variabilis) from South 

 America, deposited ; a Yellow-footed Rock Kangaroo {Petrogak 

 xanthopus), born in the Gardens. 



THE DETERIORATION OF OIL PAINTINGS' 



/^IL paintings are subject to various kinds of ch.anges, which 

 ^-^ may be considered as diseases, requiring different treat- 

 ment according to their different nature. A science needs to be 

 formed, a pathology and therapeutics of oil paintings. The 

 pathology woukl have to describe and explain those diseases and 

 their progress, and to develop the methods by which a correct 

 diagnosis could be arrived at in each individual case. The thera- 

 peutics would teach the remedies which might be applied either 

 to cure or to alleviate the disease, or at least to stop its progress. 

 A hygiene would fallow, which would have to teach how to 

 avoid pernicious influences, and which, besides, while giving 

 precepts for the technical process of painting, would have to 

 forestall those constitutional diseases which, even in cases where 

 no noxious influences can be traced, are the causes of decay, 

 after a comparatively short perio<l of existence. As medical 

 science is above all things based on anatomy and physiology, so 

 the exact knowledge of the structure of a picture would have to 

 be acquired previously to any study of its disease. Unfortu- 

 nately, direct investigation alone can procure no such exact 

 knowledge ; on the contrary, we are obliged to enter upon a 

 minute historical investigation of the material as well as of the 

 technical methods adopted by artists of diflferent schools and 

 different periods. 



The excellent works of Cennino Cennini, Merimee, Sir 

 Charles Eastlake, Mrs. Merrifield, and others, have already 

 furnished most valuable material ; but still the field for investi- 

 gation remains unlimited ; for, in order to enable us to secure 

 the conservation of each valuable painting, we ought to know 

 exactly how it was made. The artists of the present time would 

 spare infinite trouble to the investigators of future times, if, 

 along with their works, they would leave the accoiint of their 

 practice in the case of each picture. A treatment without exact 

 knowledge of the normal condition, as well as of the nature of 

 the disease, is, as we shall see, as dangerous for the picture as it 

 would be in the case of living beings. 



Professional restorers of pictures admit this danger in a 

 general way ; each of them, however, is convinced that he him- 

 self, by his personal knowledge, skill, and care, knows how to 

 avoid it. The public pays too little attention to the subject, and 

 therefore it occurred to me that it might be useful to give a short 

 account of what we know about this question, of the changes to 

 which oil paintings are exposed, as well as of the means either 

 to avoid or to cure them. 



We have to consider, first, the material on which the artist has 

 painted, that is, as far as oil painting is concerned, principally 

 wood and canvas. 



' Paper read at the Royal Institution, Friday, Ma'cli i, by R. Liebreich 

 M,D., M.R.C.S., M.R.I. 



Secondly, the priming, that is, the substance with which the 

 surface was prepared in order to be made fit for painting. 



Thirdly, the painting itself, that is, the pigments and vehicles 

 used for it, and the liquids that were added during the painting, 

 the mediums, megfuilp, siccatire, varnish, essential oils, &c. 



Fourthly, the coat or coats of varnish spread over the picture. 



The wood on which a picture has been painted may either warp, 

 or get chinks in it, or become worm-eaten, or even altogether 

 rotten. Against warping, the remedy usually applied is 

 moisture. If the panel is very thick, it is first made somewhat 

 thinner ; then the back is moistened, and the picture is left to 

 lie on its back for twelve to twenty-four hours, after which time 

 it will be found to have bent straight. Of course this must not 

 be continued longer than necessary, otherwise the convex 

 surface, instead of becoming plane, would become concave. 

 When straight, the picture is kept so by beads which have to be 

 adapted in a particular way, a certain degree of shifting being 

 allowed for the expartsion and contraction of the wood. 



Cracks in the wood are drawn together by inserting pieces of 

 wood of a special shape. 



Sublimate solutions are employed to destroy'worms. 



Trifling losses of substance are replaced by cement. Small 

 portions of rotten wood, not extending too near the painting, are 

 cut out and replaced by wedge-shaped pieces. If, however, the 

 greater part, or the whole substance of the panel, is rotten, the 

 picture must be separated from it and transferred to new wood, 

 or rather to canvas. 



This was first tried by Hacquin in Paris, and was performed 

 successfully upon many pictures, and, among others, upon one 

 of Raphael's Madonnas, in the Gallery du Louvre, and upon 

 Sebastian del Piombo's "Resurrection of Lazanis," now in the 

 National Gallery, The process no longer appears so very 

 marvellous ; it is generally executed in the following way : — 



First of all, the surface of the picture is pasted over with 

 gauze and paper. After that the wood is made straight by 

 moistening, or, if necessary, by making incisions with the saw, 

 into which cuneiform pieces of wood are driven. By means of 

 a tenon-saw the panel is to be sawn into little squares, which must 

 be 'removed by a chisel, and in this way the thickness of the 

 wood is reduced to half an inch ; it is then planed until it 

 becomes no thicker than paper, and the rest is removed by 

 means of a knife and with the fingers. The painting being 

 thus severed from its basis, it can be fixed on canvas, if the 

 priming is sufficiently preserved. In the opposite case, a mix- 

 ture made of chalk and glue, or something of the kind, must be 

 put on first, and very evenly smoothed, after being dry. This 

 done, the new canvas has to be fixed upon it by means of a mix- 

 ture of glue, varnish, and turpentine, and the substance of the 

 picture pressed tightly and evenly against it by means of warm 

 irons. 



In order to avoid deterioration, the most minute precepts have 

 been given for preparing the panel. It has to be taken from 

 the best oak, or nut-trees, or cedars. The wood is to be cut 

 into boards during winter-time, and kept till autumn before 

 being dried ; it can then be prepared only in the following 

 spring, &c. It would certainly be preferable to give up wood 

 panels altogether for large pictures, and only to think of means 

 to make the canvas stronger. For small pictures, panels offer 

 certain advantages, and can be more easily preserved from 

 decay, 



c In the canvas we meet with the [results of injuries or spon- 

 taneous decay. A rent may be mended by rags of linen stuck 

 at the back of the picture. Even a hole may be filled up by 

 pieces taken from other decayed paintings. If the picture is 

 considerably damaged, it will be best to line it. But if the 

 whole canvas is rotten and tattered, it will be preferable to 

 sacrifice it by pulling off the threads one by one, after having 

 secured the painting itself by pasting paper on the front of it. 

 This done, the painting is transferred to another canvas in the 

 same way as those removed from wood. 



There are different modes of priming, which may be brought 

 under two principal heads : the distemper and the oil priming. 



I. The canvas is distempered by a mixture of chalk or plaster 

 andripaste, or glue, which may be laid on raw, unbleached can 

 vas, or this latter may be beforehand prepared with glue or 

 paste. Several coats of this mixture must be put on in succes- 

 sion, one being perfectly dry before the next can be applied. 

 Many of the older oil paintings are painted on such grountl. 

 It has the advantage of being quicker prepared, of absorbing 

 the excess of oil, of permitting the colour to enter into the 



