[pure-silver] Re: multigrade paper is amazing
----- 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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