In the last article (August Studio Light, 1917) we defined the scale of a printing paper as the range of exposures which would just give all the tones of which the paper was capable, so that if an exposure of one second will just give the first perceptible tint on the paper, and an exposure of twenty seconds will give the deepest black of which the paper is capable, then we call the scale of that printing paper 1 to 20.

Printing papers are made in different contrasts to give different scales, the hardest papers will give all their tones with a scale of exposures of only 1 to 5, while the softest papers require a range of exposures from 1 to 100 to give the entire scale. Now the printing papers used must fit the negatives; that is, we must either have a considerable range of printing papers available to fit negatives of different scales, or else we must make our negatives, by control of the lighting and development, so that they have a scale suitable for the printing paper we wish to use. In the case of professional portraiture the latter is the usual and the correct course, the negatives are made to fit the paper, but the amateur finisher has little control over the negatives coming to him and has to keep a stock of various grades of paper to fit them.

By the scale of the negative we mean simply the range of the light intensities transmitted by it. In a very contrasty negative perhaps the blackest part will let through only 1/100th of the light transmitted by the clearest portion. In a negative of medium contrast, the densest part will let through about 1/20th of the light transmitted by the clearest portion, and in a very flat negative (one that has very little contrast) the densest part may let through as much as one-fifth of the light transmitted by the clearest portion. We should call these three scales, then, a scale of 1 to 100 for the very contrasty negative, 1 to 20 for the negative of medium contrast, 1 to 5 for the flat negative. Now, in printing, we want the printing paper to reverse the scale of light intensities recorded by the negative, as nearly as possible, so that the blackest part of the negative will be the whitest part of the print and the clearest part of the negative will be a deep black in the print; in other words, if we wish the printing paper to fit the negative we must select the grade so that when we print through the clearest part of the negative and just get the deepest black of which the paper is capable, we shall also only just print through the densest part of the negative so as to slightly tint the paper.

We see then that the scale of the printing paper must be numerically equal to the range of the light intensities transmitted by the negative.

Suppose that we attempt to print a negative upon a paper whose scale is much longer than that of the negative. Suppose for instance that we try to make a print on a paper having a scale of 1 to 20 from a negative that has a scale of only 1 to 5. We must time the printing so that the densest part of the negative is just printed through, because, if we underprint, all the tones will be too light and the print will lack detail, and if we overprint the whole print will be too dark. Now, in this case only five times as much light will pass through the thinnest part of the negative as will pass through the densest part of the negative. But the paper requires that twenty times as much light should pass through the thinnest part of the negative as passes through the densest part of the negative in order to give its deepest black in the shadows and only a tint in the highlights, so that, instead of getting a whole scale of tones from white to black in the print, such a paper restricts us to a scale ranging from a white to a gray, the densest part of the low scale (1 to 5) negative being rendered white in the print and the clearest part only gray and not black.

In Fig. 1 this state of affairs is illustrated in the curve. We see that instead of the negative enabling us to give the whole range of tones available on the long scale paper it only gives the range from white to a medium gray. The broken curve shows that by using a short scale paper corresponding to the negative we can obtain the full scale of tones by printing the short scale negative on a short scale paper. Fig. 2 is a reproduction of an actual print in which a negative has been printed on a paper having too long a scale for its contrast.

On the other hand, if we print a negative on a paper having too short a scale then we must lose some of the tones of the negative. As is shown in Figs. 3 and 4, we can reproduce the high and middle tones correctly but obtain our shadows blocked up, or, as is shown in Figs. 5 and 6, we must sacrifice our highlights in order to retain a correct rendering of the shadows.

From An Artura Iris Print By E. L. Mix New York.

From An Artura Iris Print By E. L. Mix New York.

From An Artura Iris Print By E. L. Mix New York.

From An Artura Iris Print By E. L. Mix New York.

The Photographic Rendering Of Tone Values V By Dr  StudioLightMagazine1917 197

Fig. 1.

The Photographic Rendering Of Tone Values V By Dr  StudioLightMagazine1917 198

Fig. 2.

The purpose of making a photograph is to obtain a good print, and we must adjust our procedure throughout to the scale of the printing paper to be used so that we shall get a negative the scale of which will fit the scale of the printing paper and enable us to make the most of the full scale of tones available in a print.

The control of the scale of the negative begins in the lighting of the subject, and although if the subject is one which has too great a range of contrast we can shorten the development of the negative and so obtain a negative which can be printed upon our usual printing paper, yet in practice such modification of the development is dangerous. It requires much experience and skill to obtain really satisfactory results and it is better not only to work to a given printing paper, but also to work with a fixed time of development and a developing solution of constant composition used at a uniform temperature, the lighting and the composition of the subject being arranged so that the scale of the negative obtained is adapted to the printing medium employed. The accuracy of reproduction and quality of the print will then depend upon the evenness with which the paper will give its full range of tones; that is, upon the length of the straight line portion of the curve of the printing paper. As we saw in the last article, Artura Iris paper is particularly distinguished by its long range of even tones, so that we shall obtain prints of the highest quality if we make our negatives to fit the scale of Artura Iris paper, choosing, of course, a negative making material, such as Seed 30 plates, having a very long straight line portion in its curve and so having the capacity to reproduce accurately the scale of tones occurring in the original subject.

The Photographic Rendering Of Tone Values V By Dr  StudioLightMagazine1917 199

Fig. 3.

The Photographic Rendering Of Tone Values V By Dr  StudioLightMagazine1917 200

Fig. 5.

The Photographic Rendering Of Tone Values V By Dr  StudioLightMagazine1917 201

Fig. 4.

The Photographic Rendering Of Tone Values V By Dr  StudioLightMagazine1917 202

Fig. 6.

From An Artura Iris Print By E. L. Mix New York.

From An Artura Iris Print By E. L. Mix New York.