RE: Gum hardening: top down experiment

I think this is because the emulsion is thinner and the color paler, so can
exposure caused hardening to reach the base. For the purpose of this
testing, it is preferable to have a thicker and darker emulsion (emulsion
used in a loose sense here) because then with limited exposure, the one
exposed from the back would still give image but not the one from the front
if hardening is from top to bottom, or the other way around if hardening is
from the top.

I myself feel that hardening is from top. I think the reversal of tone can
be explained by other physical property, but that is separate subject.

Dave S

-----Original Message-----
From: Katharine Thayer [mailto:kthayer@pacifier.com]
Sent: Wednesday, April 12, 2006 6:22 PM
To: alt-photo-process-l@usask.ca
Subject: Re: Gum hardening: top down experiment

On Apr 12, 2006, at 12:54 PM, Katharine Thayer wrote:

>
> On Apr 11, 2006, at 11:18 PM, Dave Soemarko wrote:
>
>>
>> The set exposure time for our test would be the minimum time required
>> to make reasonable gradation when exposure is made from the back. For
>> example, one could expose so that 4 steps are obtained. Then use the
>> same exposure time for exposing from the front with the step tablet
>> covered with a piece of mylar. The idea is that we shouldn't
>> underexpose such that both cases will not work or overexposed so that
>> both will work.
>>
>
> This seemed simple enough, so I used the same gum/pigment mix I used
> the other day (ivory black mix plus a drop of Prussian) and used step
> tablets as you suggested, covering the front-exposed tablet with mylar
> to control for the effect of exposing through mylar, and exposing them
> both for the time that the back-exposed print was exposed the other
> day, while I busied myself cleaning out the chemicals cabinet in the
> studio.
>
> But this time I apparently brushed the coating slightly thinner,
> because the color is paler and both prints were overexposed.
> They've been developing for more than an hour and they look pretty
> much the same so far: both have released the unhardened gum from
> steps 21 down to 11 and steps 1-10 are all the same tone, on both.
> So I fear I've gotten into your last category, of overexposing to
> the point that both work. I'll leave the strips to develop
> longer, while I go do some other things, but it's clear that this
> isn't going to make the clean distinction (one works and the other
> doesn't) you were hoping for.

I finally took these test strips out of the water, after 3.5 hours
development. They were both exactly the same: some blocked steps, then four
steps of decreasing tone, then blank (except for the numbers of course) from
step 11 through step 21.

Katharine
Received on Sat Apr 15 20:05:41 2006