Volltext Seite (XML)
THE PHOTOGRAPHIC NEWS. Voz. XII. No. 512.—June 26,1868. CONTENTS. PAGK Dirty Plates 301 Cellodio-Chloride for Printing on Ivory - 302 Permanent Albuminized Prints 302 Keeping and Dating Collodion • 302 Pictorial ETect in Photography. By II. P. Robinson 303 Photographic Printing in Silver, Theoretical and Practical. By W. T. Bovey 304 Photo-zincography in Practice. By J. Waterhouse, R.A 306 MSB Remarks upon the Carbon Process. By Dr. H. Vogel 308 Modified Photographic Pictures - 309 Printing by Development 309 Correspondence—Photographs of the Moon—The Transmission of Actinism by Light—Permanganate in the Nitrate Bath —The Coffee Preservative—Wet Photography in the Field without a Tent—Modes of Toning 309 Talk in the Studio 311 To Correspondents 312 DIRTY PLATES. Perhaps few troubles are more mortifying to the photo grapher than those arising from dirty glasses, a mortification which is much intensified if a few good new glasses to fall back upon are not in stock, or readily procurable. We re cently spent some hours in the studio of a first-class photo grapher in the provinces, who had suffered seriously from the trouble in question, and witnessed its operation under more than usually irritating circumstances. A stock of patent plate had been ordered and received from a reputable Lon- don house. On trying the glass, however, it was found im possible by any mode of cleaning the plate to obtain a clean negative. The defects were unusual in character, and bath and collodion were at first in turn condemned. Unlike the well-known defects produced by dirty glasses, these con sisted in fine, straight, transparent lines, varying from half an inch to 2 inches in length, sometimes vertical, sometimes horizontal. The most careful examination of the glass before producing the negative showed no indication of a defective or imperfectly cleaned surface; but whilst the chemicals were working very well in all other respects, giving rich, vigorous negatives, it was impossible to get rid of these markings. As it became manifest that the glass was in fault, recourse was had to a stock of old patent plate-glass from which some negatives had been cleaned. This glass had under gone a careful treatment with the bichromate of potash and sulphuric acid mixture recommended by Mr. Carey Lea. But now a new series of troubles arose: the ordinary markings of dirty plates were plentiful. The powerful detergent action of the above preparation was insufficient to remove the traces of former use, and mottled stains of increased opacity were apparent in every instance, chiefly noticeable in plain back grounds, where stains are fatal to the character of a picture. Other modes of cleaning were tried, employing strong acids, and strong alkalies, tripoli, &c.; but in no case was perfect immmunity from stain? secured on the old glasses. In the meantime a new stock of patent plate had been ordered from another house, and after a hasty cleaning a plate was tried, and a perfectly stainless negative was the result. We saw half-a-dozen negatives tried with plates taken at random from each group of glasses. The first in every instance gave the straight lines first described ; the old glasses invariably gave mottled stains ; and the new lot of patent plate invariably gave perfectly clean negatives. The only conclusion to which we could come regarding the first examples of the patent plate giving the fine lines was that it was imperfectly polished in the manufacture, and that little grooves existed in the surface too fine for observation, but in which lodged some trace of the cleaning or polishing material, which, lurking there, was inimical to photographic action, and so caused the transparent lines. Dealers and pho ¬ tographers alike should be on their guard against such a sample of glass; but not knowing its history we can only offer a vague caution. It was a little cheaper than the sample patent plate upon which perfectly cleaned negatives were taken ; but the difference in price was not sufficient to account for marked difference in quality. Regarding the old glasses which had been cleaned, it is to be observed that it is difficult to prescribe a plan of cleaning which shall be certainly efficient in all cases, inas much as in some samples of glass the dirt is not merely on the surface, but in combination with it, and can only be re moved by the removal of the outer surface of the glass. We have at times had striking illustration of this in opal glass, which, after having been used and carefully cleaned, has, on standing in the light, gradually shown traces of the image which had been in the collodion film long since cleaned from its surface. The silver salts in some cases clearly enter into combination with the glass; the salts of iron also have a special action on the surface, the effects of which are difficult to remove, The best detergent we have used in such circumstances has been nitric acid and water in equal parts, applied with a rubber of woollen cloth or drugget rolled up and tied tight, so as to permit the end of the roller to be used on the glass. This, followed by rotten stone and alcohol, has rarely failed in our hands; but it is possible that it may not be efficient in all cases. Perhaps in the most obstinate cases the use of dilute hydrofluoric acid would be the most certain cure. By the careful application of this dilute acid the first surface of the glass will be re moved, leaving another polished surface underneath. The difficulty to be guarded against is the production of an un even though polished surface, not equal to the perfectly plane surface secured by the mechanical grinding and polishing which patent plate undergoes. In using hydro fluoric acid its exceedingly corrosive action on the skin should always be borne in mind. An excellent piece of advice in regard to old glasses has at times been given, to the effect that the best treatment to which they can be submitted is to place them under a hammer and destroy them. The cure is certain, but costly. Photographers who are in the habit of using patent plate glass in sizes of 12 by 10 and upwards naturally hesitate before deliberately destroying plates of glass, each of which may have cost two shillings or more. A more economical remedy is therefore desirable. Happily, under the worst of circumstances, a cheap, simple, and certain remedy is at hand. Dirt was defined by the late Lord Palmerston as “ matter in the wrong place.” This definition admirably meets the case in point. The matter which is on the dirty glass is in the wrong place emphatically, because it possesses chemical action, and either increases or reduces the amount of silver reduced, and so causes an opaque or transparent mark. If it were quite