1 It; 



DISC.OVICUY 



suspected of luiving been tampered witli. It was 

 noticed that the figure of a nun in the foreground on 

 the right was not in harmony with the other personages 

 (Fig. i), and as the canvas had been presented to a 



"ROYAL CHILD AT PRAYER." 

 Fifteenthccntun- picture in the Loux-tt. 



certain rehgious establishment by a nun, it was thought 

 to be more than likely that this kneeling praying lady 

 with \Ahite cap and rosary was a portrait of the donor, 

 added by a painter who came long after Engelbrechtsz. 

 Dr. Heilbron radiographed the " Crucifixion," with 

 the result predicted : beneath the clumsy addition was 

 the original figure, that of a praying monk, in perfect 

 harmony with the rest of the picture (Fig. 2). Apart 

 from this revelation, radiography served the useful 

 purpose of showing the artist's own brush-work before 

 restoration and enabled this work, which unfortunately, 

 as is the case with all very ancient pictures, had become 

 indispensable, to be more skilfully restored to its 

 present state, as shown by Fig. 3. 



W'orking in accordance with the indications given by 

 Faber and Heilbron, and guided by his own great 

 experience as a radiographer. Dr. Andre Cheron — to 

 whom, let me say in passing, I am indebted for the 

 illustrations accompanying these lines — has consider- 

 ably advanced the science of the radiography of pictures. 

 Here, in a few words, is the principle of his method ; I 

 quote from his communication presented to the Academy 

 of Sciences, at Paris, by Dr. Lippmann, at the sitting of 

 January 3, 1921 : 



" \\'e know that the degree of transparency of bodies 



to X rays depends on the number and weight of the 

 atoms of which they arc formed. Now. in the case of 

 a picture, there are three things to be considered : the 

 supjjort (canvas or panel of wood), the priming with 

 which this support is covered, and finally the colours 

 composing the picture. 



" The support is always very transparent, but canvas 

 much more than wood. 



" As regards the priming, it appears to result from 

 the documents we possess on the subject of the making 

 of colours and the preparing of canvases and panels 

 that the old painters primed their supports with a 

 mi.xtureof carbonate of lime and glue, which is relatively 

 transparent to X rays. At the present day, on the 

 contrary, painters use, almost exclusively, a priming of 

 white lead, which is much more opaque. 



" As to the colours used by the artist to compose his 

 subject, they are also of atomic weight, and consequently 

 of a most variable transparence to the rays. Some, 

 such as white, are and have always been almost ex- 

 clusively composed of heav}- salts, of lead or of zinc ; 

 therefore they are a serious obstacle to the passage of 

 the rays. Others, sucli as bitumen and most of the 

 blacks, are extremely light and allow the rays to pass 



Showiag damaged background. 



two 



through very easily. Finally, between these 

 extremes, we find a whole series of intermediaries. 

 "But a certain number of colours which were formerly 



