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

[henk thijs <henk.thijs@hetnet.nl>]

Hi Keith,

I picked several gumcurves from the net to start with.

Made a gumprint and 'corrected' with Photoshop the negative according to the results of the gumprint until i was happy with the result.

This i did with the tools Photoshop offers (brightness/contrast, curves, shadow/highlight etc.)

So in the end -after producing several paperbasket gumprints- the result was a negative delivering MY perfect gumprint, with MY specific monitor, Epson printers, paper, paint etc.

This negative i inverted into a positive.

Now i had an 'original-positive' and a 'gum-positive'.

I downloaded a stepwedge , attached this to the 'original-positive' and started messing around with the tools of Photoshop to produce the above mentioned 'gum-positive'; as a side-effect i had an adjusted stepwedge.

Next i opened a new stepwedge next to the 'gum-manipulated-one', opened in PHOtOSHOP ADJUSTMENT/CURVES and transported step by step the manipulated one to the fresh one; the result was my gumcurve. This the one i use every time for gum and oilprinting.

It looks a bit confusing, but it is really an easy thing to do if you have once  'your perfect gumnegative'.

For the ink-and-printer settings: Dan Burkholder has really very easy  tutorials 'how-to', and they are really easy , cheap and no need to invent the wheel again. Check his website.

Succes, and if my explanation is not as easy as i think it is, please do not hesitate .... :-)

Henk

ps by the way: for my tricolors negs:

invert the positive, split-channel, invert all three to a positive and now i use MY gumcurve to produce the final negs.

On 18 okt 2008, at 20:59, Keith Gerling wrote:

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?

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