Re: Gum calibration (was: Paper negatives- Ink Selection)
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?
On Fri, Oct 17, 2008 at 6:00 PM, henk thijs <email@example.com> wrote:
> 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 <firstname.lastname@example.org> 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" <email@example.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?