Wednesday, June 18, 2008

Photographic Materials and Processes

[We are glad of the opportunity of publishing the second of the annual reports on progress in photographic manufacture which has been issued by the Society of Chemical Industry. The author is again Mr. B. V. Storr, M.Sc., of the. Ilford Company, to whom students of the technical and scientific side of photography will feel indebted for his analysis of what has been published and accomplished during the period under review, that is to say, the year 1917. We should point out that the reference "J" which figures frequently in the footnotes is to the "Journal of the Society of Chemical Industry." It will, of course, be noted that the report is one which had been completed some considerable time ago. Apparently it is not possible for the Society to bring these reviews out closer to date, although we should have thought that less than a year might be allowed to elapse before the completion of the reviewed period and the publication of the report, - EDS. “B.J.”]

           APARY from work on the production and perfecting of a antisfactory colour cinematograph process, it is probable that the chief photographic effort in the past eighteen months has been towards the improvement of methods particularly adapted to problems of the war. Exactly what has been accomplished in this direction is not yet disclosed to the general public, although some indications have been given in the form of special photographs such as those shown at the last exhibition of the Royal Photographic Society.
           On the whole the general manufacturing conditions have been getting gradually more and more difficult, although in some directions there has been an easement. Bromides, which reached a maximum price of about 25s. per lb. in 1816, have settled down again to about 5s per lb., while silver, which reached a record price of just over 4s. 6d. per os. troy, has dropped again to some what nearer its normal price. Gold chloride, on the other hand, has increased in price by about 25 per cent. Gelatine and all kinds of paper have been getting steadily scarcer and dearer, and owing to their own particular circumstances the manufacturers have found difficulty in maintaining their former standard. The condition of the glass market has compelled manufacturers to make use of renovated negative glass. The general effect of the entry of the United States into the war is not yet fully evident, but it appears highly probable that supplies of some of the raw materials will be still more restricted.
           The general position on some smaller though essential points has improved greatly. In addition to metol substitutes, metol itself is now being produced in this country as well as p-aminophenol, which latter is also being made in Canada; in Australia the manufacture of pyrogallic acid and amidol has been undertaken by a department of the government. The position in enemy countries is not known with certainly, but the patented process of Pape to resuscitate old developers by the addition of alkali is suggestive. Shering improves baryta-coated papers by a farther coating of albumen, and Luppo-Cramer makes the suggestion to improve packing papers by impregnation with manganese dioxide.
           The production of sensitizing dyes to replace those in general use before the war has been successfully accomplished by W. J. Pope, under whose direction are now being made, for Ilford, Limited, sensitol red and green (German punacyanol and pinaverdol) and a new sensitizer, sensitol violet, in addition to erythrosin and a number of dyes used for making photographic light-filters. These are being need both in this country and in the United States.

Negative Processes.

           There is little of actual progress to record in negative processes. The attempt to increase the effective speed of X-ray plates is being made in several directions, but no serious advance can as yet be reported. Baker increases X-ray speed by the use of two intensifying screens, one in front of the film, very transparent to X-rays, and one behind the film less transparent; Edwards for the same purpose proposes to coat celluloid film on both sides with emulsion. Paris and Picard have extended their patent with respect to phosphorescent substances to include the use of phosphorescent zinc sulphide as a substratum screen, a film of gelatinous alumina being precipitated on the sulphide to prevent contact with the sensitive coating.
           La Rougery has patented the production of a special negative paper by high-temperature calendering and pressure and Hudson the process of using an ordinary white paper or card for negative purposes, prints being obtained by reflected light. Sosna and Biedebach have extended their list of dyes used to prevent dark-room fog. etc., to include phenolphthalein, which turns red in alkaline developers – a process very similar in principle to the old method of using a dye in the developer.
           Several of the processes of manipulation have received considerable attention. Crabtree, of the Kodak Research Laboratory, has a paper on development high temperatures such as are frequent in tropical countries. The chief hardening agents are formalin, alum, and chrome slum, which may be employed before, during, or after development; the method recommended is to use a p-aminophenol developer, which causes very little swelling of the gelatine, followed by a plain fixing bath, a chrome-alum fixing bath, or a formalin fixing bath according to the temperature. In the experiments 95°F. (35°C.) was taken as the maximum which need be considered. An interesting method of using a two-solution developer is given by North, who treats the plate first with the solution of reducer and then with the alkali, a method which has the effect under suitable conditions of restraining the denser parts of the image and allowing full development of the light tones. p-Phenylenediamine or quinol with ammonium chloride is recommended as developer hen fineness of grain is desired, the slight solvent action of these substances on the silver salt assisting in this direction; Koch and du Prel, however, attribute the effect to a development of part only of the silver bromide granule. Brewater patents the use of the same developer, combined with nitrate, for development of a wide range of exposures; Loth substances were, of course, known already as preventives of reversal when present in the film during exposure.
           Ross, for the production of stellar images, recommends the use of a quinol and alkali hydroxide developer as giving clean-cut images, a practice in agreement with that of process workers. In this connection some experiments of Campbell and Turner are interesting. The former, by measurements of spectrograms, obtained smaller readings for the separation of pairs of lines than were given by Rowland's tables. The latter got a similar effect in crossed images of a reseau when the lines approached within a certain limiting distance and suggests some mutual effect between the images; it would be interesting to know to what extent this effect could be explained by a disturbance of the mass centres of slightly separated images by reason of the overlapping of the fringes between them, and also whether an actual slight displacement of the lines towards one another is produced in the drying of the plates by reason of the hardening of the film between the lines as compared with that on either side.
           Hechstetter has patented a combined developing and fixing bath which contains thiosulphate and glycerine, with citrate apparently as restrainer.
           The general question of fixing and washing has been examined by Elsden and Warwick. The former determined the rate of removal of thiosulphate from a gelatine film by successive washings and found no evidence of adsorption. The actual time necessary for complete removal will of course depend upon the amount of thiosulphate present, but chiefly upon the rate at which equilibrium is attained between the film and the washing water, this being a function of the nature of the gelatine film and temperature. Warwick found the same general rule to apply and examined also the behaviour of papers, where the absorbent base complicates the problem, and the method of washing in running water. In a further paper Warwick considers the rate of removal of the silver salt by thiosulphate, the normal law being again followed. The rate is dependent on the strength of the hypo solution, a maximum being reached at about 40 per cent, and a zero rate at saturation point. He used a silver sulphide tint, method for estimating the quantity of silver. His general conclusion as to the correctness of the advice usually given to fix for twice as long as is required to "clear" the film is combated by the Editor of the “Photographic Journal of America," who found that thorough washing completely removed all the silver from plates taken from the fixing bath immediately all turbidity had disappeared.
           Weinhandler and Simpson patent a method of destroying thiosulphate and salts of weak sulphur acids by means of hypochlorite produced by the electrolysis of sodium chloride solution containing prints or negatives.
           Bainbridge recommends the permanganate test as the most delicate for thiosulphate, an indication being given by degradation of tint even at a dilution of 1 in 15,000,000; the mercurous nitrate test is more affected by common impurities and indicates only up to 1 in 2,000,000.
           A considerable amount of discussion has centred round the properties of various reducing solutions, a desideratum being a reducer having an effect proportional to the depth of image. Huse and Nietz, following up a suggestion of Deck, examined the effect of combined permanganate and persulphate, and also that of hypochlorite, both reducers being nearly proportional. Becher and Winterstein have examined the action of iodine both alone and combined with thiourea and with cyanide; they give also a general classification of the best known reducers. Greenal examined mixtures of thiosulphate and persulphate, which are much steadier in action than persulphate alone. Gear calls attention to the preserving action of potassium bromide, manna, and glucose on ferricyanide solutions. Smith recommends ammonio-copper sulphate in place of ferricyanide now that the latter is so expensive.
           A paper (by Crabtree" describes the variation of flash powders with their composition, both as to the metal and the oxidiser used, with the fineness of division of the metal and with the arrangement when fired. A mixture containing sodium oxalate, red phosphorus, a metallic powder such as magnesium or a mixture of magnesium and aluminium, and a substance such as strontium nitrate, is patented by him for the Eastman Kodak Co.
Wedekind has patented the use of metals such as zirconium, thorium, and titanium, mixed with their nitrates or chlorates for the production of smokeless and odourless flash-powders.
           Crowther has examined the chemical reactions involved in the chromium intensification process first suggested by Eder and afterwards modified and expanded by Piper and Carnegie in 1905. With Eder's original formula in which a higher proportion of acid is used than in any of the modifications suggested and which leads to only slight intensification, there does not appear to be any chromium compound attached to the bleached image. In the case of the other three formula given by Piper and Carnegie, where the intensification obtained increases as the proportion of acid is reduced, the amount of attached chromium also increases; in the extreme case this appears to be partly chromium hydroxide and partly chromium trioxide, the latter imparting a brown colour, and in the other cases only the hydroxide.

Positive Processes.

           The supply of platinum is still too limited for it to be available for photographic purposes. General Thayer is said to have discovered a considerable source of it in the Adirondacks, but that has not yet materialized. The Platinotype Company have introduced "Palladiotype" in which palladium is used to give effects very similar to those of platinum, and the use of palladium as a toning agent for collodion paper facilitated by a bath which contains ammonium chloride, sodium glycollate, and succinic acid and does not require a special fixing bath, has been recommended by Valenta. The latter has also investigated the properties of salts of diglycollatoferric acid from which an excellent blue printing paper can be obtained, but of poor keeping qualities. Valenta also draws attention to the fact that Sulzberger's patent on the use of ferrocyanide (mentioned in the last report) was forestalled by Fox Talbot in 1839 and that the process was mentioned in Eder's Handbuch.
           Strasser has worked out a toning method with the use of Schlippe's salt; Schering has improved his original selenium toning bath. Nietz and Huse have worked out in some detail the possibilities of obtaining sepia tones by the use of strongly restrained developers. Very few papers give good tones by this process; the best results are obtained by a chlore-quinol developer containing bromide and metabisulphite and necessitating an increase of exposure of from 75 to 100 times that required by normal developers.
Spitzer and Wilhelm have patented a combined toning and fixing bath containing tellurous or telluric acid or their salts along with thiosulphate.
           Two patents for transfer processes have been brought out, one by Pin for film in which coconut oil soap is the chief stripping agent, and one by Kent and Middleton for paper, using paraffin wax. A transferotype bromide paper on similar lines has been introduced by the Kodak Co.
           In process and allied work, Bull, Smith, and Turner have a paper on some of the intricacies of the half-tone process, Fishenden on the photographic engraving of rollers for intaglio printing, and Crabtree on the advantage of using citric and oxalic acids respectively in the preparation of zinc and aluminium plates for lithographs. Dorian has patented the use of a half-tone screen competed of small lenticular grains, preferably coloured (see also Knudson; Ann. Rep. 1. 303). Rieder obtains an intaglio printing surface by forming a screen surface in bichromated fish glue and getting a positive over that in caoutchouc and asphalt; Orans, for ease of correction, prints on emulsion coated on a serrated surface of the type of a Levy screen on celluloid or celluloid on glass.
           Meadway uses a mixture of naphthalene and a white metal, with rubber as adhesive, as costing for a projection screen, while Bebbington coats a support such as glass, gelatine, or waxed paper with a dull blue-coloured solution and projects on to that aide, the audience facing the other side.
           An interesting account is given by Warburg of the work of Meissling on the me of dyes such as erythrosine and auramine as hardening agents in the carbon and gum processes, an effect which is attributed to the formation of formalin. The erythrosin preparations are said to be quite equal to those containing bichromate and to have better keeping qualities.


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