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Old 9th October 2017, 02:12 PM
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GoodOldNorm GoodOldNorm is offline
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Default Obsidian Aqua solution B

Solution B specifies 200g sodium carbonate (anhy) per liter. I have sodium carbonate crystal (washing soda). The darkroom cookbook gives the conversion as follows If the formula specifies sod. carbonate (anhy) and you have Sod. carbonate (crystal) multiply the amount of sod. carbonate (anhy) by 2.7 to get the correct amount of sod carbonate crystal.

sod. carbonate (anhy) 200g x 2.7 = 540g crystal

I have put 450mm of room temperature water in a 2 ltr jug,I have gradually added the crystal sod. carbonate whilst stirring for an eternity and my solution is still milky looking.
Is there a quicker way of doing this and have I got the conversion correct? What ph of solution (B) should I aim for with 200g (anhy) in 1 ltr. of water.

I have done a quick dip with litmus paper it reads ph11 , it could be higher my litmus papers maximum reading is ph11. I know litmus papers are probably not accurate enough for photographic formulas but I have not got a ph meter.
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Old 9th October 2017, 03:00 PM
Martin Rick Martin Rick is offline
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A O.1N (about 0.53%) solution will have a pH of about 11.6 Your saturated (about 20% at 20º C) will not be much more, maybe 12. The solubility decreases significantly with temperature and a 20% solution will start to crystallise if allowed to cool. (the figures are for anhydrous)

Last edited by Martin Rick; 9th October 2017 at 03:10 PM.
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Old 9th October 2017, 04:13 PM
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Problem solved, I had mixed the sodium carbonate with my tap water instead of distilled or deionised water, because my tap water is hard and full of lime scale this caused the milky precipitate. I have now mixed part (B) with deionised water and laboratory grade sod. carbonate 200g/ltr. The Sodium Carbonate (anhy) dissolved into the water with less than 5 mins. of stirring.
I also found a website https://www.onegoodthingbyjillee.com...hing-soda.html the sod. carbonate that had a milky appearence will be put to good use
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Old 9th October 2017, 04:29 PM
Mike O'Pray Mike O'Pray is online now
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Quote:
Originally Posted by GoodOldNorm View Post
https://www.onegoodthingbyjillee.com...hing-soda.html the sod. carbonate that had a milky appearence will be put to good use
Glad the problem is solved. So, 10 mins with Phil and Holly on "This Morning" beckons

Mike
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