[pure-silver] Re: Silverholes... was Pinholes in Lith
- From: "J.R. Stewart" <jrstewart@xxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Mon, 18 Oct 2004 17:38:14 -0400
I thought I'd share my solution to the problem with pinholes/pinlines on
lith.
We had a good thread last week with lots of comments and suggestions about
"normal" holey-ness of lith emulsions, pH of developers as a possible cause,
activity of different developers, and pH of alkaline fixers; even a possible
role for the use of hardening fixers to overcome emulsion defects.
I have to admit I didn't test / investigate all those suggestions. But
thanks for the ideas as I learned a lot from the discussion.
One result I reported last week was that the "holes" appeared to decrease in
abundance when I exposed the emulsion to greater degrees; the difference was
very signficant, and it lead me to try that strategy to overcome the
problem. I also said that using shorter exposures coupled with longer
developing time did nothing for reducing the number of holes/lines, even tho
max density was greater.
I'm using lith to make masks and these require lots of density. Guidance on
making them was to make an interpositive that looked like a "weak" positive
of the negative. I earlier used a 5 second contact exposure and 5 min
development. The mask I created from this interpositive was exposed at 10
sec and developed 5 minutes: this gave me a mask full of obvious
pinholes/lineholes in the densest parts of the mask.
Over the weekend I took a different approach. I made a more contrasty
interpostive by exposing at 20 seconds and developing for 1.5 - 2 minutes. I
then contact exposed the mask using this interpositive for 40 seconds, and
developed it for 2 minutes.
The result was a dense mask where I wanted it dense and zero density where I
wanted zero.. and very very few pinholes, which were very very small. This I
think I can live with.
I have no explanation for this effect except this. When I examined the
pinholes/pinlines under magnification (thanks Ryuji), they looked like 'tiny
dust particles"... I suspected that not seeing them with added exposure
might be due to more light bouncing around and under them, exposing more of
the emulsion with more light, and thereby reducing their blocking effects. I
was very careful to remove what dust I could before exposure, but these
looked as it they came embedded on / in the emulsion or way too small to
remove by physical means.
Anyway, that was my fix to the problem.. hope it helps someone else.
Jim
----- Original Message -----
From: "John Black" <jblack@xxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, October 14, 2004 9:42 AM
Subject: [pure-silver] Re: Silverholes... was Pinholes in Lith
>
>>
>> TF-3 is just sodium metaborate and sodium sulfite. According to the 20
> mule
>> team people a 0.5% solution of Sodium metaborate gives a pH of 10.8 at
> 20C.
>> So the question is how much does the hypo and sulfite change that?
>
>
> Na metaborate (Kodalk) and Na sulfite in a ratio of 4:1 by weight gives a
> pH
> of about 10.00. I would not want to use a fixer, or any post develop
> traetment at this pH. NH4 thiosulfate works just fine at just above
> neutrality.
>
> JB
>
>
>
>
>
>>
>> Nick
>>
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