[pure-silver] Re: DELTA 100 AS REPLACEMENT FOR Tmax 100
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Tue, 8 May 2007 09:18:43 -0700
----- Original Message -----
From: "Janet Cull" <jcull@xxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Tuesday, May 08, 2007 5:38 AM
Subject: [pure-silver] Re: DELTA 100 AS REPLACEMENT FOR Tmax
100
Wow! Beautiful.
Is it that film developer that is a stain dev. or the paper?
I've
never heard of such a thing.
On May 7, 2007, at 11:55 PM, mail1 wrote:
Bob, Very nice. I have explored Barry’s developers. The
non linear
blue blocking stain has posed interesting changes in the
variable
contrast filters interaction with paper contrast. It has
taken me
some time to understand this relationship. In fact this
has created
an interesting diversion from my day to day activities.
Grade 2
filtration is no long grade 2.
Jonathan Ayers [mail1@xxxxxxxxxxxxxxxxx]
It is the film developer which causes a stain image. By
"blue blocking" above is meant that the stain blocks blue
light. Because variable contrast papers have a component
which is sensitive to blue light and another which is
sensitive to both blue and green the effect of the stain is
to vary the contrast depending on the density of the stain.
At least, this is the theory. If it works the effect is to
lower the contrast of the highlights. Actually, the stain
_is_ linear in that it is exactly proportional to the silver
density, however, its effect on the paper depends on the
stain density so its effect is greater for highlight than
for shadow areas.
Most staining developers contain Pyrogallol as the
developing agent but other developing agents can also
generate a stain image, it depends on the developer formula.
Because the stain is produced as the result of the reaction
products of the developer the amount of sulfite in the
formula is important. Sulfite tends to reduce the amount of
reaction products so staining developers can not have too
much sulfite or the stain will not appear. This tends to
make staining developers relatively short lived. Note that
other anti-oxidants than sulfite are used in developers but
they all have the same effect on staining.
Staining developers were quite popular until the 1930's
when non-staining developers began to be preferred because
their results were more predictable and consistent. Except
for the highlight contrast reduction effect there are
probably not many virtues to these developers now. One
problem is determining the effective density because it will
depend on the spectral sensitivity of the printing material.
Some users beleive that the stain image reduces the
visibility of the film grain.
The stain image from Pyro type developers is a _pigment_
not a dye and is probably more stable than the silver image.
Another effect sometimes seen when Pyro developers are
used is a slight increase in edge sharpness (acutance)
beacuse the Pyro also differentially hardens the gelatin
causing an image-wise variation in index of refraction.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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