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

Katharine,
My gum mix for exposing from the back was as follows:
5cc of carbon black (lamp black) stock solution. To my best knowledge this
solution is 5% carbon in 14 Baume gum. I think it is a 5% solution, but the
label has fallen off and I can't be certain. I only use commercial gum
solutions.
Anyways I added another 5cc of 14 Baume gum and 2cc of saturated ammonium
dichromate to the mix.
Marek

>From: Katharine Thayer <kthayer@pacifier.com>
>Reply-To: alt-photo-process-l@usask.ca
>To: alt-photo-process-l@usask.ca
>Subject: Back-exposing on plastic (was: Re: Gum transfer
>Date: Mon, 17 Apr 2006 12:46:40 -0700
>
>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 Tue Apr 18 08:04:15 2006