From: Wayde Allen (wallen@boulder.nist.gov)
Date: 05/30/00-02:34:28 PM Z
On Mon, 29 May 2000, Jarred J. McCaffrey wrote:
> I would like to experiment with some very large (handmade) negatives in
> homebrewed cameras. Carbon has been touted in more than one book as being
> a faster printing emulsion than silver based processes. E.J. Wall wrote
> of a formula for carbon transfer which only required 1/4 second exposure.
>
> Is it the experience of list members that carbon gelatin emulsions are
> potentially faster than handmade (not commercial) silver based emulsions?
I can't say that my pigmented gelatin (carbon) emulsions are very fast.
Carbon is typically a contact printing process for the same reasons as the
other alt processes, and have similar exposure times.
I once did try exposing a sheet of carbon tissue in my 4x5 camera. I did
get what looks like a useable negative, but the exposure time was 2 hours!
> Is there a faster process that might better suit the handmade film
> purpose?
To the best of my knowledge, silver gelatin is the fastest chemical
process that we know of.
> Whether or not carbon is the ideal choice, I would greatly
> appreciate postings of fast carbon emulsion formulas from your experience
> or advice on creating a fast carbon emulsion.
You probably want to consider subscribing to my carbon mailing list
<http://rmp.opusis.com/mailman/listinfo/carbon>. Several of us have been
brainstorming ways to improve on the process, and possibly make it faster.
I also have a comparison of some carbon tissue recipe's and other bits and
pieces of info at <http://rmp.opusis.com/carbon/carbon.html>. I'm working
to expand this collection of data as my time permits. If nothing else,
you might be interested in the gallery of carbon images
<http://rmp.opusis.com/carbon/gallery.html>.
> As a starter here are two fast carbon emulsions from E.J. Wall's _The
> History of Three-Color Photography_. I have quoted the text exactly.
>
> (p 692)
>
> W. Wadhams, A. Ziehm, H. A. Sonderman and P. Woithe patented a
> modification of the dichromate sensitizer, which is stated to give great
> speed in printing. One formula is:
>
> Potassium dichromate 30 g.
> Magnesium chloride 10 g.
> Sodium acid phosphate 5 g.
> Water 1000 ccs.
One of the guys on the carbon list is preparing to test this recipe.
Possibly in the next week or so.
- Wayde
(wallen@boulder.nist.gov)
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