Re: Dichromate dilution and speed

Katharine Thayer wrote:

>Footnotes #1 and #2:
>
>1. Just want to make sure everyone understands that I'm not drawing any
>conclusion from this about what Sam's results might be if he did the
>same comparison, (it could be absolutely anything; I wouldn't dare to
>venture a guess) or much less about Sam's method itself. He's a master
>at his method, and the master's tools always work best in the master's
>hand. The negative I used printed a nice image, with good contrast
>(considerably more contrast than the image I was using the other day)
>using saturated dichromate. Without doubt if you start with a negative
>that has been created with the diluted concentration in mind, the
>results will be quite different.
>
>2. And also wanted to make sure everyone understand that my purpose is
>not to defend any particular way of doing things, it's only to try to
>figure out where the truth lies on a particular issue. I've been accused
>of defending turf; this makes no sense to me, as I have no turf to
>defend, unless fairness constitutes a turf. That turf, I will defend.
>
>I print with saturated dichromate but that doesn't mean I think everyone
>should. It's just the way I do it, and I'll do it this way as long as I
>print gum, because I'm so comfortable with it I can do it without
>thinking. Enough rambling,
>kt
>
>
>Katharine Thayer wrote:
>>
>> Drum roll........
>>
>> Okay, my curiosity got the better of me and I've spent the day comparing
>> saturated to diluted dichromate using a digital negative (everything the
>> same as the other day except the negative) and I'm prepared to say that
>> though I've happily printed all kinds of negatives with saturated
>> dichromate, never noticing any great differences between them (but
>> understand, I work intuitively, not by measuring, so I may make
>> intuitive adjustments for the different materials without realizing it)
>> the behavior of the digital negatives when you start messing around with
>> concentration is TOTALLY WEIRD. I can't make heads or tails of it.
>>
>> The weirdest part was that the prints I made with the diluted
>> concentration were lower in contrast (that's what I said, LOWER
>> contrast) than the ones made with saturated dichromate. I thought I must
>> have made a mistake in measuring and got too little pigment or too much
>> water in the solution, so I dumped it out and re-measured everything,
>> but I got the same result the second time.
>>
>> The other thing is that none of the 5 exposures (1x,2x,3x,4x,and 5x the
>> exposure time of the good print made with saturated dichromate) made a
>> good print; while there was an image on the paper at the end of each of
>> the times except for 1x, in no case were the tones or the relationship
>> between them correct, and their badness didn't seem to have any
>> meaningful trend in terms of exposure, so there was no way to evaluate
>> which was the best exposure of the four. If I were to give a wild guess,
>> I'd guess that around 3x might be about right, but it's just a wild
>> guess. (I know, it would be better to show this than to tell it, but
>> that would require walking back out to the studio to see if the prints
>> are dry, and I'm too tired to move.)
>>
>> There's no way I would draw any conclusion from this as far as
>> dichromate dilution and speed except to say that all bets are off when
>> it comes to digital negatives, and that I'm much more willing now to
>> believe that if Sam is printing at "about the same" time with the
>> diluted as with the saturated (I didn't follow all the hedging about how
>> long is way longer and how long is about the same, so I don't know where
>> that all came down, but as for me and my house, 5x is WAY longer, and 3x
>> is way longer, and 2x is still twice as long, for heavens' sake, which
>> is hardly "about the same" in my book) then the digital negative may
>> well be the cause.
>>
>> Katharine

Katharine,

Let me congratulate you on your tests. It is good to see that some
gum printers have the curiosity to experiment with their materials.

My own belief is that the secret to Sam's method can not be found
*primarily* in the fact that he uses digital negatives, or for that
matter that he uses gum on top of cyanotype. I say that because, as I
mentioned in an earlier message, I tested his coating in conjunction
with testing of other processes and light sources that I carried out
in preparing my article on UV light sources that is now at
http://unblinkingeye.com/Articles/Light/light.html. Tha data you can
find in that article casts serious doubts on suggestions made by some
that the reason Sam's method works is because he uses thin negatives
of low contrast. If you look carefully at the explanation of the
testing procedures that I used you will find that I made all of the
tests with a standard Stouffer 4X5 continuous tone step wedge, and
with a variety of light sources. With the gum test a five minute
exposure gave Dmax at Step 4 with two light sources, and at Step 5
with the other two. So, using a continuous tone negative the gum test
was over-exposed by about 1.5 -2 stops. Had the exposure been
corrected to give Dmax at about Step 1 or Step 2, as would be
appropriate for printing real life negatives, correct exposure would
have been about 2.0- 2.5 minutes. Also, if you look further at the
data you will see that the exposure scale of of the tested material
was quite long, about 11-12 steps, or about log 1.05 to 1.20. And
this was regular gum, not gum over cyanotype.

Sandy King
Received on Tue Dec 2 19:01:56 2003