kodak sb-8 citric acid stop bath

[Peter Schrager]

I want to make this stop bath for prints but need to know which citric acid I need to buy at the health food store...anyone have an idea; please!!
thanx, Peter

 

[Photo Engineer]

Peter, Kosher sour salt will do just fine, but you may need to adjust the pH a tad either way with acid or base.

PE

 

[naeroscatu]

Here in Canada I bought citric acid from the bulk store (Bulk Barn - not sure if you have that in USA) and it works well. Many retail food stores have bulk sections, just ask for citric acid.

 

[Peter Schrager]

stop bath

kosher sour salt...never heard of it;only kosher salt....is all citric acid the same?? I have a bunch in Ct. but I'm not there imo....
Best, Peter

 

[Photo Engineer]

Sour salt is citric acid. Kosher salt is not. Almost all Sour Salt on the shelves here is Kosher.

Citric acid can be associated with up to 3 counter ions which can render it increasingly less and less acidic. The pure acid is quite acidic, but addition of sodium ions render it more and more alkaline as the acid forms the sodium salts. Usually in a stop bath you buffer it with sodium citrate at a pH from 4.5 to 6.5 by the addition of alkali such as sodium carbonate or sodium hydroxide until it reaches the desired pH.

PE

 

[Matthew Gorringe]

And I thought I could just use a 2% solution....

Is pharmaceutical grade citric acid likely to need buffering and where do the sodium salts come from, tap water?

 

[tom_bw]

Ilford Ilfostop

I want to make this stop bath for prints but need to know which citric acid I need to buy at the health food store...anyone have an idea; please!!
thanx, Peter

Hi Peter:

Perhaps you can simply used Ilfostop, as itis citric acid based:

http://www.ilfordphoto.com/products/product.asp?n=43&t=Fixers+&+Sundry+Chemicals

I assume you want to try this because it doesn't smell. Ilfostop is virtually odourfree. I can only smell it if put my nose about an inch away, and it is not that bad smelling...

Tom

 

[Photo Engineer]

For all practical purposes, Citric Acid can be used alone.

PE

 

[Richard Wasserman]

I use 1 tablespoon of citric acid per liter of water when printing and it seems to work just fine. I get it from The Chemistry Store: http://www.chemistrystore.com/Chemicals_A_F-Citric_Acid.html

Richard Wasserman

 

[Steve Goldstein]

Sour salt is citric acid. Kosher salt is not. Almost all Sour Salt on the shelves here is Kosher.

Citric acid can be associated with up to 3 counter ions which can render it increasingly less and less acidic. The pure acid is quite acidic, but addition of sodium ions render it more and more alkaline as the acid forms the sodium salts. Usually in a stop bath you buffer it with sodium citrate at a pH from 4.5 to 6.5 by the addition of alkali such as sodium carbonate or sodium hydroxide until it reaches the desired pH.

PE

Is there any practical value to buffering? Perhaps it increases the capacity? SB-8 exhausts rather quickly IIRC.

The SB-8 formula is 15 grams of Citric Acid and water to make 1 liter. How much sodium carbonate (which I've got) would you suggest as a buffering agent? I don't own a pH meter.

Thank you.

 

[Matthew Gorringe]

Is pharmaceutical grade citric acid likely to need buffering and where do the sodium salts come from, tap water?

Sometimes I'm stupid, the developer obviously.

 

[Photo Engineer]

Is there any practical value to buffering? Perhaps it increases the capacity? SB-8 exhausts rather quickly IIRC.

The SB-8 formula is 15 grams of Citric Acid and water to make 1 liter. How much sodium carbonate (which I've got) would you suggest as a buffering agent? I don't own a pH meter.

Thank you.

Buffering increases capacity, but citric acid is inexpensive and you can replace the bath easily.

The 15 g/l is used because more might be too acidic and less would be less acidic and have less capacity. As noted, carryover of sodium salts from the developer would tend to raise pH and buffer the stop, so replenishment with more fresh stop would be quite effective for a while.

Without a pH meter or pH paper strips, I would not suggest experimentation. Just use the recommended formula.

PE

 

[Ashfaque]

Two simple queries:
(1) Is the 15% citric acid, mentioned in the KB-8 formula, refers to monohydrous or anhydrous form?
(2) I just bought a 20 grams vial of monohydrate citric acid for 20 BDT (=~ 15 Pence) from the local shop (from the food section). Is the conversion rate: anhydrous = 1.17*monohydrous (=> 17% more)?

Best,
Ashfaque