M. Pia's original negative was taken on an Edward 50 x 60 gelatine-bromo isochromatic plate (sensitive to yellow). He used a yellow screen, and a Voigtlander lens, with a diaphragm having an aperture seven millimetres in diameter. The exposure lasted eighteen minutes, with the light evenly distributed. The lens was opposite the centre of the Shroud, which is reproduced without any distortion. The plate was developed with oxalate of iron, and fixed with hyposulphite in the ordinary way. The photograph also includes the case containing the Shroud, and part of the altar, which had been temporarily erected above the high altar of the Cathedral. The negative is excellent in every way—very finely graduated, very transparent. It has not been intensified. All the markings are clearly visible, just as we have described them. This negative is so precious that M. Pia only used it to obtain a positive on glass, from which he in turn procured a negative. These two plates were intensified, which in no way altered the picture, the only effect being to make it easier to see the details. It is from this secondary original negative that all the subsequent prints, on paper or on glass, were obtained by direct printing, the Shroud only being reproduced.
M. Pia also took two smaller photographs. One of these was taken by electric light, with five minutes' exposure, and gives the whole altar, with the Shroud diminished to the length of 13 cm. 5 mm. The other was taken in daylight, with forty-five minutes' exposure, and gives a large portion of the choir, with the entire canopy, and in the background the Chapel where the Holy Shroud is habitually preserved. On this photograph the length of the Shroud is 5 cm. 8 mm. Both photographs were taken on isochromatic plates, without a screen, and they sufficiently establish the veracity of the first precious negative. The general appearance of the Shroud is identical, and even the details are distinguishable.
The same may be said of a negative taken by M. Felice Fino, which he lent us for a fortnight. It had not been intensified, and we took two prints from it on paper. M. Fino's plate is 21 x 27, and the length of the Shroud on it is 13 centimetres. The whole altar is shown, and part of the carpet which covered the paved floor of the choir. There are also a fireman standing beside the altar, and two kneeling figures in the foreground. Add to these the instantaneous photographs reproduced by P. Solaro in his book, the duplicate of which he has been kind enough to send us, and you have the whole photographic evidence upon which our work is based.
In 1534 the Holy Shroud was strengthened by a lining of linen. In 1694 Sebastien Valfre replaced this linen lining by a black material. Finally, on April 28, 1869, the Princess Clotilde herself changed the lining, which had become worn, and replaced it by a new one of crimson silk. Thus it would have been impossible to photograph the impressions transparently through the substance of the Shroud, even if it had been desirable to do so. This is not all. Pere Sanna Solaro, in his work which appeared in 1901, reproduces on page 142 an instantaneous photograph taken by one of the visitors present at the Exhibition of 1898. This valuable photograph shows the frame of the relic placed on the altar, the altar itself, and the first three rows of spectators. In this photograph the Holy Shroud and the impressions on it present the identical appearance which they do in M. Pia's fine prints. We may affirm, then, that this instantaneous photograph was not obtained by transparency.
M. de Mely admits that the plates of 1898 are genuine and normal as far as the photographic process is concerned. The argument we now have to combat is that the photographic plate has not given us a faithful image of the object itself.
The first of these critics, M. Lajoie, founds his argument on a phrase used by M. Loth in his pamphlet of 1900: " When a photograph is taken of any person or thing, the image obtained on the sensitive plate, which appears after development, is, in consequence of the inversion of tones and the reversion of positions, the negative of the person or thing— that is to say, the contrary of what it is naturally ; it is always and necessarily a negative impression, because there is nothing in nature which is not positive. Here, by a unique exception, the impression on the Holy Shroud has produced on the photographic plate a positive."
This passage contains an error. There are certain cases when, by over-exposure, it is possible for a plate to bear a positive impression, that is to say, the exact reproduction of the object photographed, without any reversal of values. M. Loth's contention is that it is not unlikely that such conditions were realized in 1898, and that in this way may be explained the whole of the, as he thinks, ridiculous fuss made about the impressions on the Holy Shroud.
M. Pia's plate, however, is incontestably a correct negative—the black traces of burning are white ; the pieces of white material used to patch the burns are black ; the borders of the lozenge-shaped patches are light in colour, in harmony with the tone of the cloth. If M. Lajoie had not at his disposal the original photographs of M. Pia, he had only to examine the illustrations in M. Loth's pamphlet. He would have seen all this at a glance.
We have already referred to the instantaneous photograph taken at the public Exhibitipn, a facsimile of which was referred to above as reproduced by P. Sanna Solaro. In an instantaneous photograph there can be no question of inversion by over-exposure. Figure 16 of Pere Solaro's work confirms Plate iv. of our work ; in it the marks on the Holy Shroud are visible in negative. And yet in other respects the instantaneous photograph is positive and normal; there is the white marble altar, and the back view of the three rows of spectators is quite natural. Inversely, figure 15, in Pere Solaro's work is equivalent to our Plate v. In his figure 15 the altar is black, the dark heads of the spectators are white, and, as these spectators are nearly all of them ecclesiastics, the marks of the tonsure on their heads are shown by dark circles. But on this figure 15, which is a perfectly correct negative, the modelling of the figures on the Holy Shroud are represented as positive, exactly as they are shown on the plate taken by M. Pia.
Thus M. Lajoie's objection, although given with all semblance of scientific truth, is valueless. Its author wishes to reduce all the problems raised by the Shroud of Christ to a mere confession of photographic error. The apparent mistake, however, is not that of the photographer.
We will now examine M. Chopin's objections, contained in a letter addressed to M. Chevalier, who inserted it in his Etudes Critiques, after having first requested Professor Lippmann, Member of the " Academie des Sciences " to be good enough to verify the assertions therein. Professor Lippmann examined the photographs, and recognized that the plate was normal and that the images of the Holy Shroud were incontestably negatives.