Re: printing gum on glass (for Marek)
Hmm, interesting question. I actually used doubled my usual
dichromate "load" for this experiment yesterday; instead of 1 unit
saturated ammonium dichromate: 1 unit gum/pigment, I used 2 units
saturated ammonium dichromate: 1 unit gum/pigment. I had gotten
intrigued lately, as a result of a discussion on another forum, with
Demachy's suggestion to use more dichromate solution when working
with a heavily-pigmented mix, so I've been trying that lately with
PBk11 (magnetic or iron oxide black) which is a fairly weak pigment
that takes a lot of pigment to make a solid black. Since that's the
pigment I picked to use for the glass experiment, and since my stock
mix of that pigment is very heavily pigmented and stiff, I went
ahead and tried it that way again.
If you go the other way, to less dichromate, it will be interesting
to compare results.
On Jul 27, 2007, at 10:49 AM, Marek Matusz wrote:
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.
From: Katharine Thayer <email@example.com>
Subject: Re: printing gum on glass (for Marek)
Date: Fri, 27 Jul 2007 10:14:25 -0700
>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:
>>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 <firstname.lastname@example.org>
>>>Subject: Re: printing gum on glass
>>>Date: Wed, 18 Jul 2007 00:17:59 -0700
>>> >Marek, what dichromate concentration are you using? that would
>>> > a difference, of course, to the exposure . Also, the
>>> > intensity from place to place. If I remember right; you're in
>>> >Houston? Your sun is probably more intense than mine in the
>>> > Northwest. I lived on the coast when I last did exposures in
>>> >sun for gum on glass; as I recall they were a minute or less
>>> > fairly heavily pigmented mix of lamp black; that's with
>>> >ammonium dichromate.
>>> >I tried exposing from the back on regular picture glass, after
>>> >thread about back-exposing on plastic a year ago or more, and
>>> >that while the exposure worked well (the gum adhered well to the
>>> >glass with back-exposure) the thickness of the glass between
>>> >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
>>> >that's the best way to go for printing on glass, as you say, but
>>> >needs to be the right kind of image that won't suffer too much
>>> >not having direct contact between the negative and the emulsion;
>>> >perhaps a composition depending on abstract shapes rather than
>>> >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
>>> >>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
>>> >>were short, and I remember long development times as well. I do
>>> >> think I optimised it. The project was never finished as one
>>> >>my stack of plates crashed and I never started again. I was
>>> >>tempted to do some gum on glass with the back exposure. This
>>> >> give a nice continuous gum layer sticking to the glass. If
>>> >>have a colimated UV light source that would be the ideal way
>>> >>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.
>>> >>good guess would save some calibration tests.
>>> >>Marek Matusz
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