[pure-silver] Re: multigrade paper is amazing
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Thu, 8 Nov 2007 15:13:42 -0800
----- Original Message -----
From: "Shannon Stoney" <shannonstoney@xxxxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, November 08, 2007 10:16 AM
Subject: [pure-silver] multigrade paper is amazing
I just did an interesting experiment. I printed a stouffer
step tablet on Ilford warmtone multigrade paper, beginning
at #00 filtration and ending at #5 filtration. I found out
that the paper scale varies not a little bit, but a whole
lot!
After printing the step tablet, I read its values on a
densitometer. I found out that at filtration #00, the
paper has a scale of 1.5. It printed about 12-13 steps
between say zone 3 and zone 7. On the other hand, at
filtration #5, it had a scale of only 0.47 and printed
only 4-5 steps between zone 3 and zone 7.
This is pretty amazing to me. How does it do it? I know
that it has something to do with the layers of emulsion.
But still.
--shannon
I just asked Dava Valvo the same question. I have seen
two explanations of how VC paper works. One was in a manual
of photography written by one of Ilford's people (Jack
Coote) the other is in many places. Coote's explanation is
that there are two layers or components which are of the
same contrast but different color sensitization, the other
explanation is that there are two components or layers of
different contrast and different sensitization.
The differece in sensitization is the key whatever the
difference is in the emulsions. One emulsion is sensitized
only to blue light, the other to blue and green. The overall
sensitivity is also different. When exposed to blue light
(magenta filter) both emulsions are exposed, when exposed to
green light (yellow filter) only the green sensive emulsion
is exposed.
In modern VC paper the emulsion components are mixed
together in a single coating although I think the early VC
papers had two coatings of different types.
I will await Dave's definitive explanation.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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