Sorry Richard, Your question and Shannon's are completely different. Your is "How" and Shannon's is "Wow"!
Regarding Richards question. I like to keep answers simple. You can get there many ways. The order suggests history of sophistication. Here's three or four.
1. Make a high contrast, blue sensitive emulsion and coat it. Make a slower blue sensitive emulsion and coat the grains in the kettle with a low contrast green dye. Coat this on top of the blue emulsion. Phase two > use laminar flow coating and coat at the same time with thin layers.
2. Make the same emulsions as above in two different kettles. Mix them together and coat them in one layer.
3. Make a big batch of high contrast blue emulsion and add just enough low contrast green dye to the kettle to coat half (or some other ratio) of the blue crystals but not all of them. This is called 'starved' sensitization. Coat this in one emulsion.
Note: You can not take a high contrast blue emulsion, sensitize it with a low contrast green dye and get a variable contrast system. You get what ever contrast you sensitized it to with the green dye. That's how you get graded papers.
Regarding Shannon'sI wish more people did what you did. Use a step tablet and densitometer. Now you really have an understanding of photography / sensitometry / densitometry. It is the best way to calibrate your system. I did that for each of my enlargers and for each paper I use with the enlarger because the results are all different. Filtration #1 is not "contrast grade 1" (as in the old graded papers). It is just a filter number. If you really want to understand the zone system, contrast and printing you need to do what Shannon did. Let's face it ...it is not important what "contrast" you get when using a filter but what "log exposure range" you get. To find that out you use your enlarger, your filters, your paper, and your chemistry and build the results. If "Pure Silver" lets me, I will attach a chart I made up for Polymax Fine Art paper (discontinued...boo hoo). You will see the difference between my enlargers and filters using the same box of paper and chemistry. The most important things in the chart is not the performance but rather the contrast grade numbers and the LER or "Log Exposure Range" shown just under the contrast grade numbers. In Shannon's data, she showed a scale range of 0.47 using a 5 filter. This is LER. You should be proud to have a system working as fine as that. 0.47 is a 5+ contrast level that many darkroom experts would die for. Their system is so out of whack yet have never tested it and live in bliss. Then wonder why can't they get high contrast. So Shannon I see your question as different than Richards. You have good magenta filters, a good light source and a fine set up so that you are able to get everything out of the paper that it is capable of giving on the high end. But you are limited on the low end at 1.5...barely making a 0 contrast. Most likely it is the paper.
Dave----- Original Message ----- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx> Sent: Thursday, November 08, 2007 6:13 PM Subject: [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 amazingI 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!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.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.--shannonI will await Dave's definitive explanation. --- Richard Knoppow Los Angeles, CA, USA dickburk@xxxxxxxxxxxxx =============================================================================================================To unsubscribe from this list, go to www.freelists.org and logon to your account (the same e-mail address and password you set-up when you subscribed,) and unsubscribe from there.
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