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SENSJTOMETRY 1 J U
negative contrast are naturally later compensated for by the degree of positive contrast desired by the individual producing companies. It is not amiss to state here therefore, that the average value of negative gamma combined with the proper positive gamma is productive of very high quality photographic results.
It might be well to state here that there are definite reasons for the actual magnitude of negative and positive gammas. Negative emulsions generally are of high speed and low contrast and gammas of the order of 0.65 are normal for the present day type of negative emulsions when developed in the present day negative developers. In other words, in working at gammas of this value we are working in the normal range of the film. In considering positive film we have an emulsion of an entirely different sensitivity characteristic than in the case of negative. This emulsion is normally of high contrast and slow speed. When used at gamma values in the neighborhood of 1.80 to 2.00 it is working in its normal region. These statements are made with the idea in mind that possibly the mental question would be asked, why are positive and negative gammas limited to the values as quoted.
It is important at this point to state a condition which exists as regards negative in the various laboratories, which is somewhat unique when we consider the present day practices as compared with the practices of five years ago. Reference is made particularly to the type of negative developer. Almost without exception the so-called "borax type" developer is used. Prior to the issuance of the borax formula each individual laboratory had its own "pet" negative formula. These various formulas agreed only in that they contained similar chemicals, although compounded quite differently. At the present time, however, the general practice is to use the original borax formula modified slightly to accomodate the requirements of each laboratory. Naturally, the strength of the formula used in a developing machine is somewhat less than that used for the rank and tank type of development. The point to be emphasized however, is the fact that practically all of the laboratories are using the borax formula with the constituents recommended and with the proportions of the various chemicals in a nearly constant ratio. This formula is tabulated here.
Formula D-76 Elon 120 grains
Sodium Sulphite (E. K. Co.) 14 ounces Hydroquinone . 300 grains
Borax 120 grains
Water 128 ounces 1 gallon
Temperature of developer 65 °F
The name "borax developer," of course, is somewhat of a misnomer inasmuch as the borax is only an alkali and is substituted in place of the usual carbonate in the developer. Along with the borax is added several times as much sulphite as was heretofore used in developers. These two constituents together with the two developing agents, elon and hydroquinone, make up the elements of that developer. It