U of S | Mailing List Archive | alt-photo-process-l | Re: printing gum on glass (for Marek)

Re: printing gum on glass (for Marek)

Hi marek,
Yesterday I printed gum on glass with sun exposure from the back. I used plain glass that wasn't treated with any sub, or even cleaned particular scrupulously for that matter, exposed for one minute, and the gum adhered to the glass quite well; there was no flaking or frilling of the hardened gum layer. But the layer was so well exposed that there was no image even beginning to appear after two hours soaking, and I needed the sink for something else, so I started brushing away at the gum to see if I could get the image to come out. The initial gentle brushing seemed to be revealing a continuous tone image that wasn't noticeably softer than the same image printed on paper, but then I brushed too hard and brushed the image right off the glass. I'll have to try this again if the sun comes out again this afternoon.

On Jul 19, 2007, at 7:34 AM, Katharine Thayer wrote:

Hi Marek,
Hope it stops raining soon.

I was pretty sure I had reported that experiment to the list at the time, so I went to the archives and searched for the post to refresh my memory about the particulars. but couldn't find it.

Anyway, I don't remember the details exactly, and I must not have kept that experiment since it wasn't among the gum prints on glass that I unpacked the other day; I must have scraped the gum off the glass and re-used it. It may be that I did that print inside under the photoflood bulb rather than outside under the sun; I just don't remember. I think there's nothing for it but I'll have to do it again to be sure. It's been raining here this week too, although we had a couple of 100-degree days last week (that would have been the time to do this experiment).


On Jul 19, 2007, at 6:50 AM, Marek Matusz wrote:


My typical dichromate concentrations are usuallu lower, for 1 volume of 14 baume gum/pigment I use 1/2 to 1/3 volume of saturated ammonium dichromate solution. The dichromate concentration definitely changes exposure, but I would say you ball park estimate of yours and mine of about 1 minute sun exposure would be a good starting point. It has been raining in Houston forever and I am keeping my fingers crossed for this weekend to get some sun.

I was surprized by your comment that you lost sharpness with back exposure through the glass. DIrect sun creates such a sharp shadow edge that I thought there should be no sharpness loss over a thin piece of glass. I guess the experimentation will show.
Thanks for your comments.


From: Katharine Thayer <kthayer@pacifier.com>
Reply-To: alt-photo-process-l@usask.ca
To: alt-photo-process-l@usask.ca
Subject: Re: printing gum on glass
Date: Wed, 18 Jul 2007 00:17:59 -0700
>Marek, what dichromate concentration are you using? that would make
> a difference, of course, to the exposure . Also, the variation in
> intensity from place to place. If I remember right; you're in
>Houston? Your sun is probably more intense than mine in the Pacific
> Northwest. I lived on the coast when I last did exposures in the
>sun for gum on glass; as I recall they were a minute or less with a
> fairly heavily pigmented mix of lamp black; that's with saturated
>ammonium dichromate.
>I tried exposing from the back on regular picture glass, after our
>thread about back-exposing on plastic a year ago or more, and found
>that while the exposure worked well (the gum adhered well to the
>glass with back-exposure) the thickness of the glass between the
>negative and the gum resulted in a loss of sharpness and detail,
>which didn't work very well with the image I chose. I still think
>that's the best way to go for printing on glass, as you say, but it
>needs to be the right kind of image that won't suffer too much from
>not having direct contact between the negative and the emulsion;
>perhaps a composition depending on abstract shapes rather than fine
>On Jul 17, 2007, at 11:59 AM, Marek Matusz wrote:
>>Good to hear the list is alive. I will miss the APIS activities
>>this year. I really wanted to go this year, but something came up
>>last moment. As far as the gum on glass I have tried it last
>>summer. I made a couple of very thin blue layers for the
>>preparation for tricolour gums. With very thin layers my exposures
>>were short, and I remember long development times as well. I do not
>> think I optimised it. The project was never finished as one day
>>my stack of plates crashed and I never started again. I was very
>>tempted to do some gum on glass with the back exposure. This should
>> give a nice continuous gum layer sticking to the glass. If you
>>have a colimated UV light source that would be the ideal way to
>>make gum on glass. Direct sun exposure is another possibility,
>>which I might try this weekend. What is the typical direct sun
>>exposure (not in the shadow) if anybody is using this method. A
>>good guess would save some calibration tests.
>>Marek Matusz

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