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#41
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DiXactol Tests
UC wrote:
PATRICK GAINER wrote: Maybe we're on the same page now. However, the VC paper does respond differently to different yellow densities. I agree, it is not a matter of color changing the contrast of the paper's emulsion. Each part of the emulsion has its own contrast characteristics. No, not true! According to Ilford: "MULTIGRADE papers are coated with an emulsion which is a mixture of three separate emulsions. Each emulsion is a basic blue sensitive emulsion to which is added different amounts of green sensitising dye. Thus, part of the mixed emulsion is sensitive mainly to blue light, part to blue light with some sensitivity to green light and part to both blue and green light. All parts of the emulsion have the same contrast. They also all have the same speed to blue light, but naturally, the part of the emulsion with only a small amount of green sensitising dye has a low speed (that is, is less sensitive) to green light. When the paper is exposed to blue light, all parts of the emulsion react and contribute equally to the final image. This image is of high contrast because of the additive effect produced by three emulsions with the same speed and contrast. The resultant curve has a narrow exposure range and is thus of high contrast." What this means is that the bluer the light, the more parts of the emulsion react. Adding two or three images of the same density and contrast in effect gives more contrast, as you can tell from working in Photoshop layers. The filtration determines which part or parts get exposed and the negative determines to what degree. The analysis gets complicated when the filtration is proportional in some way to the silver density of the negative. That's what I said before. If you restrict the light to the blue wavelengths by using the stronger (more magenta) filters, the contrast of the print may go up, but not necessarily in the same way over the entire tonal range: the highlight areas may look 'odd'. If we were to put the blue color separation filter in the projection path of a yellow image, it would print as a gray negative of some contrast.br /body " Nevertheless, since the yellow filter is also called minus blue, a yellow density in the negative causes less blue light to hit the paper, thus acting as if it were some value of gray for any blue sensitive part of the emulsion. Therefore, a stain image that is yellow does in fact act as a negative of some degree of contrast and will print as a flat negative on VC paper. Thus, the yellow stained image of a proper pyro negative, where the stain is proportional to the silver image, will have higher contrast on VC paper than would the same silver image without the stain. The contrast of such a negative will thus be higher on graded paper or any blue-only sensitive paper than on VC paper of current construction. The stain part of this same negative can be separated from the total by bleaching in Farmer's reducer to remove the silver. It will print, albeit with lower contrast, on both graded and VC paper. Maximum blue-pass filtration will sometimes make a satisfactory print from the stain portion of a pyro negative, as will grade 5 paper. What is all the argument about? We cannot by exposing a piece of VC paper in our darkrooms determine if the paper has separate layers of different contrast or a more simple mixture of emulsions, all of the same contrast. We really should not have to decide. We simply follow the manufacturer's instructions. |
#42
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DiXactol Tests
PATRICK GAINER wrote: Nevertheless, since the yellow filter is also called minus blue, a yellow density in the negative causes less blue light to hit the paper, thus acting as if it were some value of gray for any blue sensitive part of the emulsion. Therefore, a stain image that is yellow does in fact act as a negative of some degree of contrast and will print as a flat negative on VC paper. Thus, the yellow stained image of a proper pyro negative, where the stain is proportional to the silver image, will have higher contrast on VC paper than would the same silver image without the stain. True, depending on the color and density of the stain, etc. The contrast of such a negative will thus be higher on graded paper or any blue-only sensitive paper than on VC paper of current construction. True. It can neverprint exactly the same on VC paper as on graded paper. Raising the contrast by using magenta filtration will cause non-lineraities, due to the fact that the silver image and the satin image differ in color transmittance. The stain part of this same negative can be separated from the total by bleaching in Farmer's reducer to remove the silver. It will print, albeit with lower contrast, on both graded and VC paper. Very faintly on VC paper with normal filtration (2-3 grade filter). Maximum blue-pass filtration will sometimes make a satisfactory print from the stain portion of a pyro negative, as will grade 5 paper. What is all the argument about? The original poster wondered why his pyro did not give him the density he expected. I explained it was because he was using VC paper, where the stain contributes little or nothing to the printing density. We cannot by exposing a piece of VC paper in our darkrooms determine if the paper has separate layers of different contrast or a more simple mixture of emulsions, all of the same contrast. We really should not have to decide. We simply follow the manufacturer's instructions. |
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