Re: Gum calibration (was: Paper negatives- Ink Selection)
Keith, I am not following every message exchange with Loris, but i have the impression that maybe , just maybe , there are things influencing the exposure times which are not mentioned: I think you are using the obvious 'browning' tubes, or? I do, and my times are about 100 seconds for transparencies and about 500 to 700 seconds (humidity is a real factor) for paper (or foil) negatives (for oilprinting you have to double the times). But very important is of course the distance between the tubes and the paper to expose ; do not forget that if you vary the distance the exposure times are increasing 'square' (Is it the correct word for: distance two times, exposure times 4 times ?) . Cyanotypes with paper negatives never worked for me; even exposure times of 20 minutes were not ok (yes, i know there is a max there). One word for the curves: I did programming for a living and after that i do not want to invest lots of time in learning programs , so if i can avoid that, i do. I worked on one negative during weeks with Photoshop , to tune it for gum until i was really happy with the result. I inverted it to make a positive; opened the original positive again with a stepwedge, messed around with all the tools Photoshop offers, until both positives were the same. Result: a stepwedge for a good gum; now i opened a 'clean' stepwedge next to the manipulated one, and with the CURVE tool in PHOTOSHOP you can step by step bring the 'gum-stepwedge' to the 'clean-one' and the result is a GUMCURVE; that is the one i use now everytime. Hope this helps, Henk On 18 okt 2008, at 0:26, Keith Gerling wrote: I'm not sure if there is a humidity factor. I just never paid any particular attention to it. I gave special scrutiny to Loris's print because I was looking for differences in our procedures in my quest for shorter exposure times. My development time for Fabriano is about the same. On Fri, Oct 17, 2008 at 4:56 PM, ender100 <ender100@aol.com> wrote:Is printing out with gum like Platinum/Palladium? The more moisture, the
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