Back-exposing on plastic (was: Re: Gum transfer

Okay. Well, so far I'm not getting it to work, so there must be
something different either in my materials or my method. I'm now
getting a good solid gum layer that is probably overexposed because
it takes forever to develop, but I'm getting really uneven results. I
have one print on mylar that is coming out quite high-contrast
(losing highlights) just like a heavily-pigmented coating would be
if it were front-exposed. And another, that was coming out very
well, very delicately continuous-tone, but then, after 35-40 minutes
of exposure, started developing pinprick holes all through the gum
layer, so the image is all full of these little holes. And contrary
to your report, I'm finding that streaks and unevenness of coating do
show up in the print. (My coating is very heavy, lamp black heavily
pigmented and coated thickly so as to be completely opaque.)

I suspect that my problem is that I'm exposing too long and hardening
the layer all through (I don't get black gum coming off the top as
you described the other day, and it takes a long long time before gum
starts dissolving out of the less-exposed areas of the image). Maybe
for this method it's better not to harden clear to the top of the
layer. How long do you develop your back-exposed prints?
Katharine

On Apr 17, 2006, at 12:24 PM, Marek Matusz wrote:

> Katharine,
> I don't know much about the transparency material. Just a brand
> that I picked up in a local office supply store a while back.
> Marketed by HP. Come to think of it the transparency has a gelatine
> layer on one side for injet printing, so perhaps it was pr-coated,
> subbed or somehow prepared to accept gelatine layer. I soaked it in
> chlorox to soften the gelatine and the brushed it off. Both sides
> seem to be working the same.
> Thanks for posting the image
> Marek
>
>
>
>> From: Katharine Thayer <kthayer@pacifier.com>
>> Reply-To: alt-photo-process-l@usask.ca
>> To: alt-photo-process-l@usask.ca
>> Subject: Re: Gum transfer
>> Date: Mon, 17 Apr 2006 10:53:14 -0700
>>
>> Marek, you betcha I'll add your image to my site. I'm right now
>> trying to replicate your results with the thick heavily pigmented
>> coating, with some interesting, not 100% successful, results, but
>> the one that's soaking now looks promising. I've had a very
>> difficult time getting the very thick gum layer to stick through
>> development on untreated mylar, trying to replicate your
>> conditions, and have had to retreat to the scuffed mylar. I
>> wonder if your transparencies are made of some other more gum-
>> accepting material.
>>
>> Katharine
>>
>>
>>
>> On Apr 17, 2006, at 10:44 AM, Marek Matusz wrote:
>>
>>
>>> There were a lot of interesting posts this weekend and I am
>>> going thorugh them now. I have done a few more gum transfer
>>> experiments. Here are some observations and issues.
>>>
>>> When exposing a gum layer through the substrate (glass,
>>> polyester, etc). This is "expose through the bottom mode" heavy
>>> pigment concentration is OK, coating imperfections are not that
>>> critical as the air bulles rise to the top, streaks in coating
>>> are also on the top. A thin image layer that adheres well to the
>>> substrate after development shows relatively few imperfections
>>> and looks suprizingly good. I have not done much more on that as
>>> I am waiting for a sunny weekend where I can experiment with
>>> some gum on glass.
>>>
>>> Gum Transfer.
>>> Here is how I approached it. I though it would be very difficult
>>> to transfer actual developed and hardened gum image by means of
>>> softening it and transferring to the paper. Instead a process
>>> similar to a single carbon transfer was appealing to me. Here is
>>> what happened.
>>>
>>> I coated a few sheets of plyester with same emulsion (gum, lamp
>>> black, ammonium dichromate) that I used in my previous
>>> experiments (expose through the back). This time I exposed in a
>>> traditional way from the top. I will call it the gum tissue.
>>> This should form a hardened image on top of the gum layer with
>>> unexposed and soluble gum on the bottom. We know what happens
>>> when you put this image in water. Everything just slides off.
>>> OK, I then placed the gum tissue on top of gelatine sized paper,
>>> made a sanwich let it sit for a while and placed in warm water
>>> to start dissoliving unexposed gum so that the tissue and the
>>> support could be separated. Then just wait until the water
>>> dissolves the rest of the unexposed gum revealing the image.
>>>
>>> Some of the difficulties. Even a very short water immersion
>>> (cold or warm) of the exposed tissue to remove dichromate
>>> softens and starts dissolving the gum, no usable image can be
>>> transferred.
>>>
>>> The tissue image needs to have decent mechanical strength for
>>> the transfer. It needs to be thicker, which suggest less
>>> pigment, thicker coating.
>>>
>>> All the air bubbles and imperfection are on top, where the image
>>> is formed. There are all visible in the final image. Rollesrs
>>> and other means of smooting out the coat do not work with thick
>>> layers.
>>>
>>> My impression is that because the dichromate is present in the
>>> transfer process for about 30 minuts, before tissue is pulled
>>> away, I am getting a dark reaction, or something, as I am not
>>> getting very clean highlights. My exposure might be too long, or
>>> dichromate concentration too high as well.
>>>
>>> My negatives are for Pd printing, not for carbon. Just a minor
>>> issue.
>>>
>>> As Sandy noted I could print in carbon, but it is such a finicky
>>> process that requires a very precise time and temparature
>>> control.. I am still hoping that an easy way of transfer could
>>> be found with gum, or perhaps gelatine/gum mix as I am thinking
>>> now.
>>>
>>> I have one picture from this trials and perhaps Katharine would
>>> be so kind to add it to her site.
>>>
>>> Marek, Houston
>>>
>>>
>>>
>>>
>>
>>
>
>
>
Received on Mon Apr 17 13:47:23 2006