RE: acetone

I'll chime in here in case Howard doesn't. When he's printing in our lab he
uses a 50:50 solution of potassium dich and isopropyl alcohol.

--Dick

-----Original Message-----
From: owner-carbon@spitbite.org [mailto:owner-carbon@spitbite.org] On Behalf
Of Sandy King
Sent: Friday, December 22, 2006 11:48 AM
To: carbon@spitbite.org
Subject: Re: [carbon] acetone

Vaughn,

Not only do you use about twice as much sensitizer as I do, but I
also use a much weaker solution. Typically when working with my high
relief tissues I use a 1% or 2% ammonium dichromate solution, so you
are essentially putting 8-16 times the amount of dichromate salt in
the tissue as I do. I am intrigued by this because based on previous
post I believe your tissue is very similar to mine in terms of wet
coat thickness and amount of pigment per given area.

Anyway, regarding the question, the more dichromate salt you put in
the tissue, the lower its printing contrast. If you tray sensitize
the tissue will continue to absorb dichromate for at least five
minutes, though about 85% of the maximum possible is absorbed by the
end of three minutes. For that reason it is best to use a standard
time, keeping temperature the same, to assure that you always have
the same amount of dichromate in the tissue.

I do not have any problem with streaking on the print with the method
of brush sensitizing I do. Another source of streaking, which folks
may attribute to brush coating, is caused by pulling the tissue from
the support to soon during warm water development. If there is any
kind of resistance when you start to separate the tissue from the
support you should return the print to the water and increase the
temperature.

Regarding Howard's hybrid method of sensitizing, is he using just
dichromate solution or dichromate solution plus some type of spirit|?

Sandy

At 10:03 AM -0800 12/22/06, Vaughn Hutchins wrote:
>Sandy and Howard,
>
>I noticed that you use half the sensitizer that I do.
>
>What changes in the print would I see (contrast/exposure), if everything
>else is kept constant and I used 15ml of sensitizer rather than 21ml for an
>8x10?
>
>Would I pick up some deeper penetration of the UV due to less Ammonium
>dichromate due to less volume used (thus less UV blocked by the yellow of
>the Am. Dichromate)?
>
>Many thanks,
>
>Vaughn
>
>PS Dick's latest post arrived as I was composing my questions. The method
>"perfected" by Howard seems to suggest that the amount is not critical --
>but perhaps I am wrong on this if Howard times his sensitizing and controls
>amount that way. Or perhaps the gelatin absorbs as much as it can and that
>gives consisantcy. Or is it strickly a matter of concentration -- not
>volume?
>
>Perhaps the larger amount of sensitizer I use helps reduce streaking?
>
>So many variables!!!!!
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Received on Fri Dec 22 18:03:03 2006