U of S | Mailing List Archive | alt-photo-process-l | Re: Gum calibration (was: Paper negatives- Ink Selection)

Re: Gum calibration (was: Paper negatives- Ink Selection)

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,

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>

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?