From: Nick Makris (nick@mcn.org)
Date: 09/27/03-06:10:56 PM Z
Ok (BTW, please correct any questionable assumption made herein), I have a digital step wedge negative with a base density reading of .39 and a highlight density of 2.2 (being a complete neophyte, I might have these reversed) which equals a difference of 1.81. As Sandy kindly pointed out recently, you also have to make an small adjustment which makes this neg have a density range of approximately 1.7. As has been discussed recently, 1.7 should be a good density for a normal negative when doing PT/PD. Also, there is good separation between all the steps when viewed and tested for density on my old color analyzer, now new densitometer.
I used equal amounts of FO (freshly mixed at 27% as I have done many times) & PD (older) and a single drop of PT (which has rendered the desired color) for a total of 11 drops on a proper sized image opening. My rough calculation is .48 drops per square inch of image area on Cranes Platinotype when using a glass rod.
The resulting test print indicates that I have arrived at nearly the proper exposure because the highlights have density up to the proper point on the steps and the highlights have cleared properly. And, the black is as black as I could ask for.
On the other hand, the dark steps loose separation beginning at 30%.
Ed Stander tested this substrate and found it to have an identical association between visible and UV light blockage in the entire range - Our thanks to and a quote from Ed:
"The film blocks a proportion of received UV and Visible light equally across the board. There are no real peaks or troughs in the transmission curves. Having said this, the blockage is as follows: The waxed film blocks 1/2 of the UV falling on it, while the unwaxed film blocks 3/4 of the UV it receives. These values (amazingly enough) are nearly exact at 360 - 400 nm."
I infer from the above statement that if I use the film unwaxed, I will add a stop of exposure to my established time plus compensation for the base. In the case above, the exposure is just more than twice the length of the exposure for a Lightjet neg that I have printed successfully many times - as expected.
So, where am I? Well that's what this post is for - I don't have any real direction to follow here and I'm looking for some input.
Could the ink blockage for the UV not be linear to the visible light (my enlarger) that I used to test the density?
Could I have miscalculated the density (complete babe in the woods here) and in reality the neg is more/less contrasty than I'm thinking it is?
Could some of chemicals be outdated? Potasium Oxylate (cold bath) which as I understand it is better as it gets older (I also tried some unused), freshly mixed Ferric Oxylate and I can't believe that the EDTA has any bearing here.
Could the single drop of PT be enough to increase the contrast of the print from an already ok (read that I'm assuming a proper contrast for PT/PD) negative?
I'm sure to be embarrassed when the simple answer is arrrived at and I promise to report.
Appreciate your thoughts,
Nick
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