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

Re: Paper negatives- Ink Selection

I never get dichromate stain with a 15% solution, even with 5-12 minute exposures.

If Keith were to increase his dichromate from pot di full strength to am di full strength, yes the curve changes and I assume he would recalibrate to make a curve for full strength. But if I remember, Keith is fairly loosey goosey about his practice and produces excellent work so he may not need to.

However, my real reason is to ask why pot di, which only saturates to say 10-13% at best, and falls out of saturation if temps fall below 70 (something I discussed LONG ago on the list relative to Kosar's chart) when using a 15% am di which would be faster than a saturated pot di and would never fall out of solution unless he were working outside in winter I might suppose because am di saturates at 30%? I remember one BJP article discussing this very fact that in England back in the day of no central heat, the pot di would actually only be about a 5% solution!

I find that people into pot di are dyed in the wool pot diers and people into am di can become the same, just because we all build our practice around our practice, you know? BUT if long exposures were an issue I just don't see why anyone dyed in the wool pot dier wouldn't switch.

What I should really do is just force myself to use pot di for a year and see if there is any benefit to it.

Now let's throw another monkey wrench in here for you to test, Loris, since you are fast becoming the expert as you are: at a certain point of percentage, am di doesn't produce a speed gain ENOUGH to warrant the increased percentage. This is why I settled on 15% tho I used to use 7.5% down south where the humidity was always 50% or greater. It's not a truly linear exposure thing, such as in the darkroom when you expose a print half a stop more or less you can expect half a stop more or less exposure (given the characteristic curve of paper this is true only to an extent, of course).

If I remember correctly, Suzanne Izzo even uses only 5% di concentration, and the interesting question is how low a di concentrate you can go and still have acceptable times. It's pretty amazing to me, actually. BUT again this has nothing to do with Keith's issue of long exposures with paper negs, just a thought I'd throw out there...

Christina Z. Anderson
----- Original Message ----- From: "Loris Medici" <mail@loris.medici.name>
To: <alt-photo-process-l@usask.ca>
Sent: Thursday, October 16, 2008 2:52 AM
Subject: Re: Paper negatives- Ink Selection

Using 2A:1B indeed gives a speed gain (w/o any significant quality loss).
What does it to the characteristic curve of the process I can't say, since
I never compared...

Keith uses oiled negatives, whereas I don't. But still can get a good
image and a nicely exposed gum layer (which develops in about 30 - 40
minutes, sometimes 60, which can withstand erasing another layer on top of
it) with only 6:30 exposure. It looks out of the line compared to mine,
and that's what makes me tend to think that it's something about DR and/or

Full strenght AD would definitely increase speed considerably. But then
(as a note) I personally don't like the characteristic curve (and results)
I get with high dichromate. I was using 20% with plain paper negatives,
then switched to 10% with translucent inkjet bond and the shadow
separation seems to be better now.

BTW, speaking about high dichromate concentration, comes to mind something
interesting to mention about dichromate stain:

I was getting dichromate stain (in darkest shadows) with plain paper
negatives, exposed for 15 minutes, 20% AD. Then I switched to translucent
inkjet bond, which - according to visible light measurement - is exactly
1.5 stop faster than plain paper. That makes 5:20 equivalent exposure time
(with 20% AD) for the new negative media. I decided to halve the
dichromate (to 10%) and increase exposure by 1/3 stop to offset the weaker
concentration (not measured, just was testing if +1/3 stop will be
enough). Therefore new exposure time became 5:20 + 1/3 stop = 6:40 (which
was cut to 6:30 later), for translucent inkjet bond, 10% AD. I don't get
dichromate stain anymore. That can be attributed to the fact that I'm
giving less exposure to the emulsion, but then I can't explain why I don't
loose even a little bit of highlight detail using the same negative and
same development time!? If I was giving less exposure (absolute) to the
emulsion, then I should have loose highlight detail, don't you think? But
I don't!?

Could it be not only absolute exposure (the total energy the emulsion
gets) but also the exposure time does have an effect on dichromate stain?
(Or what else?)

I'm not claiming anything, just sharing something that confuses me (a
lot)... Any thoughts?


15 Ekim 2008, Çarşamba, 7:13 pm tarihinde, Christina Z. Anderson yazmış:
Have you tried mixing your cyano 2A:1B to cut down one stop?

I don't think the 15 min is out of line since I use Pictorico with gum and
6 minute exposure.

Why aren't you using full strength am di? Or 15% perhaps, instead of pot
to decrease your times, too?


Hi Loris,

My gums require 15 minutes with oiled negatives.  I would really like
to reduce this.  Also, cyanotypes made with the same oiled negatives
require exposure times of 30-45 minutes.  How does this compare with
others?  It seems pretty long.