U of S | Mailing List Archive | alt-photo-process-l | Re: was Miracle size for gum now tonal range

Re: was Miracle size for gum now tonal range

Minor correction: in my perplexity I misread condition (2) although the misreading doesn't change or clear up anything. It's actually (3) that provides the pointless comparison, exposing the 2x dichromate the same as you would expose the 1x dichromate. (2) proposes to expose the 1x dichromate twice as long as you'd normally expose it, which also makes no sense to me, why you would do that. You'd just end up having to develop it twice as long to get the same final result.

So, to summarize, in case the point got lost somewhere: if the overall question is how should you compare two dichromate concentrations as to their effect on tonal scale, my answer would be just what I did for the demonstration on my website: you'd determine the correct exposure for each of the concentrations, using a step wedge, then you'd compare the number of steps printed for each of the concentrations at its proper exposure, using the same coating mix, same paper, everything else the same. As I reported in the earlier post, when I did that I found that at saturated dichromate concentration, at the correct exposure, the pigment mix printed 8 steps; at 1/5 dichromate concentration, at the correct exposure, the same pigment mix printed 4 steps. Hence my statement that more dichromate = more steps.

On Oct 11, 2009, at 12:04 PM, Katharine Thayer wrote:

As I said, I'm not understanding your argument leading to your proposed three conditions, so let me go through it and see where I'm failing to understand what you're saying. You're comparing 1x dichromate with 2x dichromate, yes? If 1x dichromate is usually properly exposed with 1x exposure, which is how I read condition (1) then 2x dichromate should be exposed with 1/2x exposure, not 1x as in condition(3) and I don't see why you would include condition (2) of exposing the 2x dichromate for the same time you would expose the 1x dichromate; that's the meaningless (pointless) comparison I mentioned above. So maybe you could clarify what you're suggesting here, because it's not making sense to me.