Re: Gum image has reversed

Bruce,
I agree with Tom here. I have done some lamp black printing recently
(Daniels Smith pigment). As suggested by Dave about 1 gram of pigment per 10
ml of standard gum solution is a good start. I have cut it down on the
pigment some more to about 1 gram in 15 to 20 cc gum. You have way too much
pigment IMO. I can't comment on the exposure since I do not use you type of
light source.
Marek, Houston

>From: Tom Sobota <tsobota@teleline.es>
>Reply-To: alt-photo-process-l@sask.usask.ca
>To: alt-photo-process-l@sask.usask.ca
>Subject: Re: Gum image has reversed
>Date: Mon, 09 Jan 2006 11:25:32 +0100
>
>Bruce,
>
>In addition to what Christine and Katharine told you, I would suggest three
>things:
>
>1. Get a Stouffer 21 steps tablet or equivalent. It is a priceless
>instrument for testing and sharing information.
>
>2. Avoid lamp black at least for your first experiments, if you can. It is
>a difficult pigment. If you must use black, use one of the others, such as
>Ivory black.
>
>3. For almost the same quantity of gum and dichromate (i.e. 2cc gum + 2cc
>dichr.) I have used 0.05g of lamp black. Even allowing for different brands
>etc. this is almost ten times less than what you have used and even so,
>under the more dense zones of the tablet I got tone inversion. In my
>opinion you are using far too much pigment.
>
>Tom Sobota
>Madrid, Spain
>
>At 05:40 09/01/2006, you wrote:
>>I'm new to the list and will apologize in advance for the barrage of
>>questions which I'm going to unleash over the next little while. My
>>frustration level is running quite high. However, for the moment, I will
>>try to limit myself to two main problems.
>>
>>First, a little background. I dabbled in gum dichromate about 25+ years
>>ago and had some satisfactory results, but never really stayed with it. I
>>always wanted to get back into it and so, here I am. I still have the 1
>>lb. jar of Potassium Dichromate I bought back then and still have some Gum
>>powder as well. Whether the age of my chemistry has any bearing on the
>>results I've experienced, I'm not sure. I really can't see how Pot Dichr
>>can "go bad" but, you never know.
>>
>>My first question relates to the first usable print I've obtained after
>>many, many failures. I finally have something that suggests I have a
>>chance of success, but the print has reversed to negative. Can anyone
>>explain this? The detail is quite good, but I have a negative, not a
>>positive. Here are some details about my method:
>>
>>>Lanaquarelle Medium Watercolour 140 lb. Paper, *not* sized
>>>Analogue 4x5 negative made in-camera on Tri-X film
>>>#2 blue photoflood light source about 25 inches from neg
>>>20 minute exposure
>>>Emulsion made from 2.5 ml gum, 2.5 ml potassium dichromate solution and
>>>about 0.5 gm Daniel Smith Lamp Black pigment
>>>Still development for about 10 minutes brought up reasonable density --
>>>my fear in letting in go on much longer was that I'd loose the entire
>>>image (just like the first dozen or so failures).
>>
>>I realize that I should probably size the paper and that Lamp Black is not
>>the best starting pigment, but I was just trying to get myself into the
>>ball park on emulsion and exposure times. However, I'm stumped by the
>>negative product.
>>
>>My second question relates to the type of gum arabic I should be using.
>>This success (if you can call a negative print a success) came after I
>>switched back to my old gum arabic powder (25+ years old). The gum was a
>>fine, white powder which I put into solution using the formula in "The
>>Keepers of Light" by William Crawford. My earlier failures had been done
>>using some Gum Arabic pre-mixed solution recently purchased from
>>Photographers Formulary. Using the pre-mix I got virtually no results --
>>anything I got was basically a "soot and chalk" type print where the
>>shadows went black and the highlights blew out. Nothing in between. No
>>detail at all.
>>
>>Can anyone explain the lack of results with the pre-mix Gum Arabic?
>>Should I stick with the powdered form and mix it myself? The fact that I
>>got *some* results from the powder suggests to me that the pre-mix is
>>somehow at the root of my earlier problems where I got soot and chalk.
>>
>>Many thanks in advance -- all advice gratefully received.
>>
>>Bruce Pollock
>>
>
>
Received on Mon Jan 9 10:33:02 2006