U of S | Mailing List Archive | alt-photo-process-l | Re: Paper negatives- Ink Selection

Re: Paper negatives- Ink Selection

Hi Keith & Katharine.

15 Ekim 2008, Çarşamba, 8:13 pm tarihinde, Katharine Thayer yazmış:
> Keith, according to Loris's post below (which I didn't get) you use
> saturated potassium dichromate for your sensitizer.  The quickest way
> to decrease your exposure time is to increase the dichromate;
> saturated ammonium dichromate should cut your exposure time at least
> in half.

Very true.

Keith, as I wrote to Chris, considerably higher dichromate concentration
change the characteristic curve of the emulsion dramatically, therefore
it's not a foolprof solution -> you may not like how the emulsion behaves
at those concentrations. (For instance, I don't like to work with
saturated AD myself...) On the other hand, the opposite also can be true
-> you may like better the emulsion's reaction to light at higher
concentrations. It's something to try and see for yourself. (I mean if
you'd want to work at higher concentrations or not.) As an experienced gum
printer, you probably know all that was written above (and settled on
saturated PD not by coincidence), therefore I assume you're looking for
something else that could help you in reducing your exposure times. Right?

I also want to add something else for those who care; I personally believe
it's not a good idea to use saturated solutions, because solution
strengths differ with temperature. The best is to settle on the strongest
"known" concentration which doesn't crystallize in your working
environment. For instance if you're sure that your darkroom / chemistry
storage won't go below 20C / 68F, and if you know that solubility of PD @
20C is 12%, then you can mix a say... 11% solution - knowing it will be
always 11% (consistent!) as long as the temperature doesn't go below 20C.

> Also, humidity is correlated directly and strongly with
> speed; I don't know what your climate is like there, but humidifying
> your workspace would speed up your emulsion, if you wanted more
> speed.  Also, in my observation masa prints slower than other papers,
> everything else being equal; that could be another consideration in
> the length of your exposures.
> ...

Also very true.

Katharine, I suggested something about coating Masa which you may have
missed. See the message in the list archive:


"...I always humidify the back and front of the paper after coating (I
quick-dry the coating with a hair drier), just before putting in the
contact printing frame (over a mylar sheet - to hinder moisture loss
during exposure), in order to get maximum speed..."

Keith, I use an ultra sonic humidifier; it's very handy for that purpose,
albeit I'm not sure it's practical at full sheet size!

BTW, I'm sure Keith knows this fact too. (I remember him talking about
exposing almost wet paper...)