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GRAININESS OF PHOTOGRAPHIC DEPOSITS-A REVIEW
D. R. White*
THE problem of graininess of developed photographic deposits is particularly important to the motion picture industry as in motion pictures the photographic images are observed normally under such magnification as to make the structure of the image an important consideration. The non-uniform;ty of deposit which is designated by the word grainin?ss may be considered as having three phases, which were pointed out by Jones and Deisch1 in 1920.
(a) Graininess due to the existence of individual particles of silver.
(b) Graininess due to the clumping of the particles.
(c) Graininess due to the agglomeration of the clumps.
The work done prior to this publication comes chiefly under (a) above, but since then the work has been extended to cover (b) and (c) also. The divis;on thus made has been generally accepted as clarifying the problem though the divisions are not clear cut and sharp. Of these three phases (b) and (c) are of more immediate importance to the motion picture industrv than fa) since it is true with present commercial emulsions that the individual grains are of such size as not to appear individually under normal conditions, while clumos and aggregates of clomps represent structural elements large enough to be visible all too frequentlv. However, phase (a) represents the limit that can possiblv be attained with photographic emulsions of the present type and should be studied by the manufacturers and research workers to provide as far as possible for further general rednct'on in graininess. Much study has also been devoted to the individual grains as a means of formulating or checking theories or views of photographic action. For all of these reason^, therefore, much appears in the literature bearing on this point. The portion of this extended literature considered here wUl be limited to the part dealing with the relation of the developed silver grain to the undeveloped grain originally occurring in the emulsion.
In a paper wp'tt<>n in 1904, A. and L. Lunvere and A. Seyewetz2 commented: "Following many works on the subiect it has uo to the present been generallv adnr'tted that the size of the grain of reduced silver in gelan'ne-bromide plates is uniform whatever be the developer used". Thev also noted that Abnev had already found the size of grain of reduced silver in an overexposed olate to be finer than in the case of normal exposure and also that additions of alkaline
*Redpath Laboratory, Parlin, New Jersey.
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