TECHNIQUE OF DEVELOPMENT 359 



the exhaustion life of the developer. Pinakryptol yellow is not suited to this use, as 

 it is affected by the sulphite of the developer. A wide range of concentration has 

 been used in the various experiments conducted. A concentration of 1 part in 20,000 

 is intermediate in this range and may be considered fairly representative. The action 

 of a desensitizer is by no means instantaneous, and a minute or so must be allowed for 

 its effect to occur. 



The tests reported in the literature do not show clearly whether or not a desensitizer 

 has a specific action on development. No large effects on contrast or emulsion speed 

 are noted, where care has been exercised to avoid bleaching of the latent image by 

 bright inspection lights. 



The action of desensitizers is presented as destruction of color sensitivity of color- 

 sensitized plates, and hence they are considered valueless with noncolor-sensitized 

 emulsions. The literature of desensitizers is not increasing so rapidly as it did a few 

 years ago, and this fact probably indicates a trend away from inspection methods of 

 development control. Actually negative emulsion speeds have increased markedly 

 and still appear to be on the increase as new products are manufactured and offered 

 to the trade. 



Time-temperature Methods. — The time-temperature method of development con- 

 trol, also known as the "thermal" system, is now widely recommended and used. 

 Its success depends upon uniformity of emulsions and developer chemicals available 

 to the photographer. Both factors are met through the present reliability and control 

 in chemical industries. Basically the method is built on the thesis that, starting with 

 a given emulsion and developer, control of the time factor will adequately govern 

 development, and, accordingly, successive exposures may be developed to the same 

 gamma by giving equal time of development. In many cases, compensation of 

 development time is introduced to allow for variation of the developer temperature 

 and for exhaustion and aging effects through repeated use. This, of course, requires 

 considerable preliminary information and rather complete study of developer and 

 development characteristics under practical conditions. Of course, it is not practical 

 for any one organization to try to cover all the variations of amateur and commercial 

 practice with all the widely different formulas available, but all the manufacturers in 

 the United States are recognizing and encouraging the time-temperature system of 

 development control by the development recommendation normally given, which 

 takes the form of a recommended time at a certain temperature in a specified formula. 



Of course, this method of development control is not the panacea of all the ills 

 and troubles of development. In the discussion of agitation of developers, it was 

 pointed out that even reproducible agitation is difficult to attain, and, correspond- 

 ingly, specification of time and temperature alone is not complete. Some indication of 

 agitation must be included to be complete. No adequate description of agitation is 

 always possible, so the more exact phrasings of development recommendations usually 

 include something to the effect that exact times for a given contrast would have to be 

 determined by trials under the actual conditions to be used. For many purposes this 

 exactness is unnecessary, and the recommendation may be followed directly with 

 entirely satisfactory results. 



Sensitometric and Test-exposure Control Methods. — In that section of the photo- 

 graphic industry where the greatest bulks are handled, the motion-picture laboratories, 

 the development control is based upon standard test exposures of various kinds. Fre- 

 quently the standard is a sensitometric exposure, and the development is controlled 

 to produce a chosen gamma with the film going through at the time. Sometimes a 

 picture, produced in standard manner is used instead of the sensitometric exposure. 

 In this case the judgment is visual, to hold the picture quality to a satisfactorj^ match 

 of a more or less permanently fixed standard. In either case, development control 



