Re: Gum calibration (was: Paper negatives- Ink Selection)
Hi Henk Thanks for your comments and thanks for sharing your work. You've inspired me to branch out! I am using 24" Sylvania UV tubes spaced about 2.5cm apart and about 5 cm away from the print. (Perhaps you mean "tanning"?) I am confused about your stepwedge procedure. It sounds as if you designed your curve without any feedback from the gum precess itself. Or was the original a scan of a print? You say that you "opened the original positive again with a stepwedge". Can you be more specific as to how you do this? Thanks! Keith On Fri, Oct 17, 2008 at 6:00 PM, henk thijs <henk.thijs@hetnet.nl> wrote: > 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 >>> more printing out? >>> Best Wishes, >>> Mark Nelson >>> Precision Digital Negatives >>> PDN Print Forum @ Yahoo! Groups >>> Mark Nelson Photography >>> On Oct 17, 2008, at 3:55:22 PM, "Keith Gerling" <keith.gerling@gmail.com> >>> wrote: >>> >>> I am going to look more carefully at my next print, but off-hand I >>> would say that I can see very little highlight detail in my prints >>> before development. I've had occasions where I could barely detect >>> any image at all, but have still come up with a full-toned print after >>> development. How long did it take to develop that print? >>> >>> -- >>> >>> >>> > >
|