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.

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.