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

Okay, then I've been using too much pigment. The prints I was making
yesterday were coming out sooty and grainy; the graininess was so
pronounced that it spoiled fine detail and fine tonal gradations.
I'll try your protocol when I can, thanks.
Katharine

On Apr 18, 2006, at 7:04 AM, Marek Matusz wrote:

> 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 09:53:32 2006