Re: printing gum on glass (for Marek)
Katharine,
It has been raining here no-stop and I have not done any printing yet. I am wondering about the dichromate concentration. Typical gum practice for paper printing uses fairly high dichromate concentrations. I was wondering if much lower concentrations would work beeter for the back exposure. Something more in line with carbon printing. I have to look up the data for back exposure on transparency that I have done last year.
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 (for Marek)
Date: Fri, 27 Jul 2007 10:14:25 -0700
>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.
>Katharine
>
>
>
>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).
>>
>>Katharine
>>
>>
>>
>>
>>On Jul 19, 2007, at 6:50 AM, Marek Matusz wrote:
>>
>>
>>>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
>>> >>
>>> >>
>>> >>
>>>
>>>More photos, more messages, more storage—get 2GB with Windows Live
>>> Hotmail.
>>>
>>
>>
>
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