In Fig. 78 is shown a range of tones made up, not as a continuous wedge, but of forty-four distinct tones. The number which can be seen in the illustration is less than the number which the eye can distinguish in a print because of the limitations imposed by the process of half-tone re-production. If the full one hundred tones which the eye can distinguish in a print were reproduced by the half-tone process the halftone illustration would look like a continuous wedge.
Fig. 78. Range of 44 Distinct Tones.
Fig. 80. Print Showing Empty Highlights.
Fig. 81. Print Showing Blocked Shadows.
In Fig. 79 the same wedge has been printed on all three papers, and it will be seen that Contrast Velox has reached its full blackness only a short distance up the wedge,
Regular Velox has gone further, and Special Velox has gone the farthest of all, so that w h i 1 e all three papers will give the same range of tones, this range is impressed on Contrast Velox with only a short range of densities in the negative; for Regular Velox a longer range is needed, and for Special Velox a still longer range. The range of densities required in a negative to just print out the full range of tones on a paper is called the "scale" of the paper and this is measured by trying an increasing series of exposures until the range of exposures which will just give the whole range of tones on the paper is found; that is, if an exposure of one second to the bare paper with no negative will just give the first perceptible difference from white paper, so as to show the first trace of tint on the paper, and an exposure of twenty seconds will give the deepest black the paper is capable of rendering, so that no increase of exposure will produce any denser black, then we should call the scale of the printing paper 1 to 20.
Thus the word "scale" applied to a printing paper does not refer at all to the range of tones in the print. It indicates the range of contrast in the negative which should be printed on that paper. A paper with a scale of 1 to 20 will require a negative in which the densest part lets through 1/20 of the light transmitted by the clearest part, because if this negative is printed on that paper the print will just have the whole range of tones from white to black completely printed out, each tone in the print corresponding to a density in the negative, and there will be no differences of density in the negative unrepresented by differences of tone in the print.
Fig. 82. Gray, Flat Print.
Special Velox has a scale of about 1 to 20 and is suitable for printing from contrasty negatives. Regular Velox has a scale of about 1 to 10 and is suitable for printing from negatives of moderate contrast, while the very flattest and least contrasty negatives, which are the result either of excessive over-exposure or underdevelopment should be printed on Contrast Velox, which has a scale of about 1 to 5.
It is important to choose the grade of paper correctly for the negative. If the paper is too contrasty for the negative; if, for instance, we print a hard negative (one that has strong contrast) on Contrast Velox, then we shall have to sacrifice a part of the scale of the negative; either we shall get the highlights empty and white, as shown in Fig. 80, or we shall get the shadows blocked up, as shown in Fig. 81. On the other hand, if the scale of the paper is too long for the negative and we print a soft negative (one that has little contrast) on Special Velox, for instance, when we should have used Regular Velox, then we shall get a gray, flat print, as is shown in Fig. 82.
With paper, as with film, the density of the picture is controlled by the duration of the exposure and the development, but whereas with films the contrast is dependent upon the time of development, the contrast increasing as the development is continued, with paper the contrast is fixed by the maker, and after a few seconds the development does not change the contrast of the print at all but only affects the density of the deposit. This is illustrated in Figs. 83 and 84.
In Fig. 83 we see that with increasing time of development, a film shows an increase in contrast, while in Fig. 84 that by prolonging development it is clear after reaching a certain stage in the development of a print there is only an increase in total density and no increase in contrast.
If a print is over-exposed, it can be taken out of the developer before it is fully developed, and if under-exposed, it can similarly be forced in development, though there is some risk of yellow stain if development is continued too long. The best results can, of course, only be obtained by getting the exposure right and giving the normal time of development, which is from 15 to 20 seconds for Contrast and Regular Velox, and about 30 seconds for Special Velox.
Fig. 83. Growth of Contrast with Development, Eastman N. C. Film.
Fig. 84. Increase of Density with Development, Velox Paper.
The matter of greatest importance for getting really first-class prints, therefore, is to give them the right time of exposure.
Before starting to print a number of negatives they should be classified for contrast so as to choose a suitable grade of paper for printing them; that is to say, put the negatives in three envelopes according to whether they are to be printed on Special, Regular or Contrast Velox. Now take the negatives in each of these envelopes and divide them again into three more classes - normal negatives having average density, thin negatives, and dense negatives. When printing, if we take the exposure for the normal negative as standard, then the thin negatives will require half this standard exposure and the dense negatives will require twice, while sometimes we may possibly meet an exceptional negative - very thin or very dense-which may require one-fourth or four times the standard exposure. Having classified our negatives in this way, in order to get our exposures right we need know only the exposure on each grade of Velox paper for our standard negatives, and if we print with a 25-watt tungsten lamp at a distance of one foot, we shall find that the exposure for a standard negative will be about 20 seconds for Special Velox, about one minute for Regular, and one and a half minutes for Contrast. These figures are to be taken only as a guide, and when a new light or a new package of paper is used for the first time, trial exposures should be made with the standard negative, giving, say, 15, 20 and 30 seconds exposure, so as to select the exposure which develops to the right density with the correct time of development.
It is best always to use the same standard negative for testing a new paper or a new printing lamp and any other new conditions that may arise in printing, as more useful information will be gained by making tests with one negative only than if a different negative is selected each time a test is to be made.
If the subject of exposure is dealt with in this way, if the negatives are classified for density before printing, and a test is made on a standard negative, it will be found easy to print a large number of negatives on several grades of Velox paper and get a very high percentage of first-class prints with normal development.
With regard to development and after-treatment of the print, there is very little to say, since the matter is fully explained in the instruction sheet that accompanies each package of Velox paper. It is best to buy the ready prepared developers such as Velox Liquid Developer or Nepera Solution and to follow the directions given.
When fixing prints, take care that they do not lie on top of one another in the fixing bath without change so that each print will get its supply of fresh acid hypo.