American cinematographer (Jan-Dec 1926)

June, 192*; AMERICAN CINEMATOGRAPHER Nineteen S. Stability. Some desensitizers which are very effective as a preliminary hath are destroyed immediately by the sulphite, if added to a developer. The stability in a developer and the keeping property of the water solution when exposed to light and air are important factors. 9. Speed of Action. Especially when a desensitizer is used in a developer the speed ofthe desensitization is important. LuppoCramer' has pointed out that while Rhoduline Red G is as strong a desensitizer as phenosafranine it takes twice as long to produce the same effect. This is probably due to a slower rate of diffusion through the gelatine. 10. Availability and Cost. For general use it is obvious that a substance must be available at a reasonable price. III. Comparative Properties of Different Commercial Desensitizers 1. Phenosafranine. The first important member of this series is phenosafranine of which the desensitizing action was discovered by Luppo-Cramer and is described fully in his book on the Safranine Process.* Many of the safranine dyes have a similar desensitizing action, but considering all its properties LuppoCramer considered phenosafranine to be the most generally useful of those which he examined. Phenosafranine has a strong desensitizing action, does not give trouble from fog, and is a well known and easily obtainable substance. It is perfectly transparent in a bright red light but has a dark appearance in a green light. It is less effective in desensitizing panchromatic materials such as Eastman Commercial Panchromatic Film than is pinakryptol green. When used with an ordinary plate such as Eastman 40 it extends the spectral sensitivity through the green giving a maximum at 580 mm. Phenosafranine forms a precipitate in developers containing hydroquinone to about the same extent as does pinakryptol green but if added with care can be used in most elon-hydroquinone developers. In pyro developers it is distinctly less soluble than is pinakryptol green. The most serious objection to the use of phenosafranine is the intense stain which it imparts to the film, trays, and hands. When a film is thoroughly fixed in an acid fixing bath most of the dye washes out quite readily. However, any residual stain left in a negative has no effect on its printing time as phenosafranine transmits the violet light to which positive emulsions are most sensitive. When used in small concentrations to prevent aerial fog its staining action is not appreciable. In Fig. 3 is shown the absorption spectrum of phenosafranine, in relation to that of pinakryptol green and basic scarlet N. 2. Pinasafrol. Pinasafrol is stated by Wall1' to be safranine J IV or tetra methyl safranine. It is said to be a slightly stronger desensitizer^ ' "■ ] l than phenosafranine but was stated by Luppo-Cramer to be less desirable for prac (Contlnued on Page 2 3) 7. Luppo-Cramer. "Protective Dyes in Desensitizing " Phot Ind. p. 187, 1925. 8. Luppo-Cramer, "Negative Development by Bright Light The Safranine Process" 2nd Edition, Leipzig, 1922. 9. E. J. Wall, "History of Three Color Photography," Boston, 1925, p. 300. This book also contains a very complete bibliography on desensitizing. 10. Luppo-Cramer, "The Best Desensitizer," Phot. Ind 1925 p. 1356. No light — no pictures! THE unusual and beautiful photography in films today ought to be a constant reminder of the imperative need for lighting absolutely under control — which Cooper Hewitt made possible. And Cooper Hewitt has continued through the years as standard equipment. It has kept pace — kept faith. And it is still the light to use, adaptable to every advancement in art. Whenever lighting worries you, get in touch with "Mike" Shannon. First aid to smooth-running production. '-% COOPER HEWITT ELECTRIC CO. HOBOKEN, NEW JERSEY Hollywood Office — 7207 Santa Monica Blvd. KEESE ENGINEERING CO., John T. "Mike" Shannon, Mgr. 144 ©C.H. E. Co., i>>i6 PARIS BRUSSELS ROME MADRID LISBON m JERUSALEM LONDON RENE GUISSART Atmospheric Shots in Any Part of Europe Taken according to your own instructions in an artistic manner to match the phography of your produclion. OFFICIAL CORRESPONDENT IN EUROPE FOR: American Society oj Cinematographers ; Frank D. Williams 118 Avenue des Champs-Elysees PARIS Cable Address: LOUVERANDE-PARIS BERLIN BUDAPEST GENEVA CAIRO ATHENS ALGIERS c DTC. »TC.