From: pete (temperaprint@blueyonder.co.uk)
Date: 03/07/03-11:06:55 AM Z
Hi,fellow paperstainers,
Dichromate stain can be very effectively removed by the use of dilute
sulphuric acid 1%/2% as I reported to the list many years ago --:
So how could I get rid of this residual stain?
A number of other chemicals were tried with no effect. Then I remembered
work I had done on bromoil years before-many bromoil bleaches contain a
small amount of sulphuric acid, which had the effect of turning the gelatine
colourless before inking, and as similar chemistry is employed I decided to
give it a try. BINGO it worked the brown stain disappeared and no green
stain reappeared, however the stain did not in fact go away. On heavy
exposure a light neutral grey tone was created, but this did not pose any
problems as it just made the colours in the shadow regions slightly darker
and in effect undetectable, in normal practice."
Bromoilists seem quite happy to use the acid as part of there technique but
gum printers run scared of this powerful chemical, which is understandable
but over reactive in my opinion, after all said and done there are many
dangerous things we do every day and don't turn a hair. For instance driving
a car cooking your dinner, consuming vast quantites of toxic food and drink
etc etc in my case beer ;--<
I have been trying out a 5% sol of sod hydroxide recently which seems to be
a viable alternative. Whilst this chemical must to be used with care we do
often clean our toilets/restrooms/WC's with it in the commercial form of
domestos,oakite and other brand names.
It is early days yet but it seems to work.
Pete
http://www.alternativephotography.com/peter_fredrick.html
Ps Drain clear also contains a form of weak sulphuric acid I have cleared my
prints with this when I have run out of the hard stuff.
> Matti,
> I never worry about the yellow stain until the end of multicoating, and
> then I clear it in the potassium metabisulfite, which is (quick and easy) 2
> tsp to 1 liter. The only problem with the yellow stain is it alters the
> true look of some colors, so that when you finally clear at the end of the
> multicoat, your print goes lighter and cooler instantly and it can be
> surprising. However, I did that 6g pigment of D Smith pinkcolor to 12ml gum
> and it comes out a sickly pale olive that made me think it was a useless
> color when I used to multicoat--and then this time, since I am only testing,
> I cleared half of a print of just that layer (totally overexposed) and got
> the most beautiful baby butt pink, next to the ugly olive green half. Moral
> of story: don't assume a color is worthless until the stain is all washed
> out or (better yet) cleared in pot metabi. ----- Original Message -----
> From: "Matti Koskinen" <mjkoskin@koti.soon.fi>
> To: <alt-photo-process-l@usask.ca>
> Sent: Friday, March 07, 2003 2:14 AM
> Subject: success!
>
>
>> hi
>>
>> first of all, warm thanks to all. Without your help, I would have never
>> made this far.
>>
>> This morning I finally succeeded making 3(!) gum prints. During last
>> week I've made perhaps about one hundred prints, and now 3 of them look
>> to me ok. The problem I had with papers was due to exposure. Now I've
>> learned that exposing with blended light lamp (a mercury vapour lamp
>> without ballast), I have to expose 1 hour and develop about 1-2 hours.
>> But exposing in direct sunlight 3 minutes is enough and half an hour of
>> developement.
>>
>> Developing longer time gives better results, as it washes also the
>> stains, a print developed only 1/2 hour is much more yellowish.
>>
>> Now it's time to start learning to make multiple coatings, but also have
>> some rest. I've been doing my prints almost day and night.
>>
>> best,
>>
>> -matti
>>
>>
>
>
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