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

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, just for clarification I assume this is powdered pigment?

  I'm using paint (Daniel Smith lamp black). At something like
45-50% paint/paint-gum mix it was too pigmented, as described in
earlier posts in this thread; last week I tried a paint/mix
proportion of about 33% and got a more reasonable print, on the back
of my last piece of 3M inkjet transparency. I also cut back the
dichromate, as per your protocol. Like the earlier prints I showed
using ivory black, the back-exposed print is much better than the
front-exposed print on transparency material, and it could be called
"fully tonal" in the sense that it has ten steps running from dark
to light, the sense that most people mean when they say you can make
a fully tonal gum print in one coat. But it's not "fully tonal" in
the sense of expressing very subtle tonal gradations in highlights
and in shadows, which is the claim that was being made for back-
exposure on gum and which I thought I saw promise for in the print
Marek showed us. In fact the skin tones on this print are
posterized, although it might not showl in the jpeg. If I were to
continue this exploration, I would use a different negative; I used
this one because it had a step tablet attached.

I've made a decision over the weekend that's going to change my life
significantly, requiring changing my place of residence, so I won't
be doing any more gum printing for quite a while while I sort and
pack and move and unpack. I decided to go ahead and show you these
prints I did last week, for whatever they're worth to anyone. I
would say from my experiments so far that the promised truly fully
continuous-tone print that can be obtained by back-exposure is
elusive, and perhaps can only be achieved by luck or at the end of a
long and arduous period of trial and error.

http://www.pacifier.com/~kthayer/html/topdown2.html

Katharine

>
>
>> 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 Wed Apr 26 09:58:58 2006