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Old 30th April 2009, 06:44 PM
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Rob Archer Rob Archer is offline
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Default Sodium Sulphite

How critical to the working of a developer is the amount of Sodium Sulphite? I was mixing a fresh batch of D76 yesterday and realised I had only 70g left. The recipe requires 100g. I understand the sulphite is a preservative and also effects the grain, but I'm not scientific enough to know why or how.

I've ordered some more from Silverprint so I could just wait for it I suppose abd add the remaining 30g, but Will the dev work just the same with only 70%of the sulphite?

If not, what adjustments to time should I make?

Rob
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Old 1st May 2009, 11:03 AM
Niall Bell Niall Bell is offline
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Why don't you just reduce the weight of other ingredients and water by 30% and make 70% of the volume of developer you'd planned on?

For interest, it's added to developers as an anti-oxidant (perservative) as in foodstuffs. High concentrations can, appartently, erode silver grains in the emulsion- but as with all of the photochemical reactions, the precise roles are not fully understood.

Niall
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Old 1st May 2009, 05:19 PM
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"Why don't you just reduce the weight of other ingredients and water by 30% and make 70% of the volume of developer you'd planned on?"

I would have done, but I only realised I'd hardly any sulphite left after I'd added the metol!


Rob
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Old 1st May 2009, 07:55 PM
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Rob, won't make much difference if you're not thinking of keeping it as stock for a long time.. Mix as is and develop; you'll be fine...
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Old 1st May 2009, 08:17 PM
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Thanks, Peter. I use it 1:1 and chuck it anyway. I just done a film in it and it's fine.

I'm still unsure what effect the sulphite has other than as a preservative though.

Thanks

Rob
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Old 3rd May 2009, 06:51 PM
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It's just a preservative. You'll find it does the same job in many products, including food...
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Old 4th May 2009, 11:16 AM
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Quote:
Originally Posted by Peter Hogan View Post
It's just a preservative. You'll find it does the same job in many products, including food...
The sulphite level is far to high to just be a preservative, it's deliberately high to also act as a Silver solvent and help produce fine grain.

However dropping the level from 10% to 7% will give a very slight increase in film speed with a barely noticeable difference in grain size, as the developer was used 1+1 it would be unlikely you'd notice any difference without running controlled tests.

Mac

Last edited by agenoria2; 4th May 2009 at 11:27 AM.
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Old 4th May 2009, 01:33 PM
Dave miller Dave miller is offline
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Out of interest I quote from the Silverprint Manual, page 5.1

Sodium Sulphite – this is the most commonly used developer preservative. It is slightly alkaline and so may sometimes be employed in fine grain low contrast developers as the only alkali/accelerator ingredient. It’s moderate use permits full emulsion speed, but used in quantities, in excess of 80-100g per litre of stock developer, it will start to have a noticeable solvent effect on the silver image, reducing grain and slightly decreasing film speed.
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Old 4th May 2009, 01:52 PM
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Many thanks for the informative replies, folks. I'm just a beginner in home-brewing and it's a steep learning curve. I do appreciate the vast pool of knowledge here.

Thanks

Rob
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