Volltext Seite (XML)
May 15, 1885. THE PHOTOGRAPHIC NEWS. yet which, in reality, were taken on a 4-4 plate, the head being placed well up to the end of the plite and the rest managed by vignetting. So with landscapes ; a negative of any given size, may, by exercising judgment, be made to produce prints ap parently one or two sizes larger. Concerning the best means for vignetting, it is not altogether easy to speak dogmatically. In the case of a negative in which there are such marginal defects as to render it out of the question to print it entire, the way we adopt is to take an oil tube of burnt umber and paint an oval of suitable form all round the plates, then apply the end of the finger as a dauber so as to diffuse the paint inwards and in such a manner as to gently and almost imperceptibly obscure the subject within a suitable distance of the extreme margin, which must be left quite opaque. This, when dry, forms a vignetting mask that yields a good effect, and which possesses this advantage that, when prints are required, there is no further trouble to be encountered in fitting masks. In portraiture, excellent effects are obtained by double vig netting, that is, first printing the subject with a vignette mask in the usual way, and then, having removed the negative, ex posing the paper to the light under such conditions that the print is shielded from the light by means of an opaque mask, the margin of which is guarded off into transparency. This gives a dark margin to the picture, but none the less is the portrait vignetted, only in this case it is vignetted into darkness instead of into light. This principle may be applied also to landscapes, often with a good effect.—Photographic Times. THE RAPID CONTACT PRINTING PAPER. BY NIORGAN AND KIDD.* THROUGII the courtesy of your Secretary, it is our privilege to address you a few words on “Rapid Contact Printing Paper,” which, since its recent introduction, has strongly engaged the attention of photographers, and has been deemed of sufficient importance to attract more consideration than any of the advances in photography since the introduction of dry plates. It is not our province as manufacturers to try to define the true value of the process, nor is it necessary, considering the very elaborate criticisms to which it has already been subjected by critics who know a great deal about it, and critics who do not. The process has been particularly liable to hasty criticism. It has not been constrained to win its way gradually into notice ; but its promise was so brilliant as to command immediate attention. This brilliancy of promise consisted mainly in its perfect freedom from two of the greatest drawbacks of the old process—its absolute dependence on a long exposure to daylight, and its distressing instability. By the newer process the ex posure is brought down to the shortest period advisable, and there are the strongest assumptions that its results are absolutely permanent. It has been complained that the manufacturers have under stated the very short exposure necessary. As far as we are con cerned, we do not find our exposures as originally require modification, but we have in some cases found failures arise from an improper estimate of the very great decrease of illuminating power of artificial light as the printing-frame is moved farther from its sources, and also from insufficient allowance for the colour of the negative, a negative of a non-actinic yellow colour sometimes taking as much as fifty times the exposure of a nega tive of a blue colour. We can hardly imagine practical workers failing to attach sufficient importance to either of these facts, but we have found it is generally to miscalculations of this kind we are indebted for accusations of understating the necessary ex posure. Exposure must always be a matter of judgment; but a trial or two is generally sufficient to estimate it. Once decided, there is no further difficulty with prints from the same negative, if your light does not vary in power. It is therefore wise to trust as little as possible to a power so uncertain as daylight ; and after trials we ourselves have decided to use magnesium ribbon, and we recommend this as a very convenient and inexpensive light. Two inches of it burnt four inches distant from the negative is sufficient for an average exposure, lasting less than a second. We have always found a short exposure to a very powerful light such as this, gives better results than a longer * A paper road at the Edinburgh Photographic Society. exposure to a lower power. It may be always ready, as a supply sufficient for a gross of prints may be carried in the waistcoat pocket, and it is certainly not expensive when two inches is suf ficient for the exposure of at least four prints, if the printing frames are arranged in a a square facing the light burnt in tbe centre. And we may here draw your attention to the economy of lighting power chemicals, &c., practicable by making single operations suffice for batches of prints. It is sometimes com plained that the operations are cumbersome, and that a print takes an unreasonable time before it is produced; but this com plaint applies even more to albumenized papor when single prints only are produced. It is only by toning, washing, and fixing in batches that the slow progress is bearable, and in the newer pro cess it is as easy to work prints in batches as singly. It is the exposure, however, which is the prime drawback in the manipu lation of the old process. While the rapid contact printing paper is totally free from this objection, it has not been able to reduce the much smaller period taken by the subsequent opera tions, and in these the time necessary to both processes does not differ materially, and in both they are simple and nearly mechanical operations. Perhaps of the two the development necessary to the newer process requires a little extra judgment; but any extra attention required is amply repaid by the power the process gives of humouring the negative. Many negatives useless with another, process may be made to give good results by treatment in development. To obtain the very best results, intelligent working is certainly required ; yet in this, as in many other processes, average care will give average results. It must also be considered that the labour is so greatly reduced that men of superior intelligence may be employed without extra expense, as they would be able to do the work in a tithe of the time required formerly. It will, however, be the aim of manufacturers to render the process as simple as possible, and we think it reasonable to look for great improvements yet in matters of detail. In such a new process discoveries are made day by day, trivial enough in themselves, but greatly improving the convenience of working. We have just found an improve ment of this description in a more efficient “ mountant.” The mounting at one time threatened to prove a difficulty, the high surface produced on the prints by being squeezed and mounted while on glass was destroyed if damped on the back with paste for mounting, and we fiud the only mountant which does not have this action is the preparation known as “ Giant Cement,” which may be made with Nelson’s No. 1 gelatine, with acetic acid sufficient to cover the bulk, dissolved with heat. A small quantity of chrome alum may be added to make the mixture insoluble. In making these few remarks we have not thcught it necessary to describe the working of our process in detail, as our formula) and method have been frequently published in the photographic journals, and are no doubt familiar to you ; but we have placed in the hands of your Secretary a number of our printed instruc tions and formula) for distribution, and these describe the whole process very fully. We may also call your attention to our specimens which were all produced with short exposures to magnesium wire and daylight, and we think it will be agreed are in no way inferior to good albumenized paper prints. We beg to thank you for your very kind permission to submit them to you. Iides. The isolation of the hitherto disputed argentous chloride, Ag,Cl, seems to have been effected in a very satisfactory manner by Dr. W. B. E. Hodgkinson, who has been ex perimenting in conjunction with Captain Abney. Normal chloride of silver or argentic chloride was ex posed to light, and after it had become thoroughly darkened the unaltered argentic chloride was dissolved out by copious washings with a solution of sodium chloride or of ammonium chloride, the argentous chloride being left behind. Not only did the argentous chloride give good analytical
