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

Re: printing gum on glass



Katharine,

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.

Marek


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  
>detail.
>Katharine
>
>
>
>
>
>
>
>On Jul 17, 2007, at 11:59 AM, Marek Matusz wrote:
>
>>Chris
>>
>>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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