ECN-2 stop bath alternative

[iandvaag]

I'm just about ready to try my first batch of ECN-2, but I have some questions about the stop bath. I can't find sulphuric acid in any concentration (not even battery acid) for a reasonable price. I found one place that would sell concentrated H2SO4, but it would cost over $130 of my worthless Canadian dollars for a litre after shipping, etc. was factored in. I was wondering if I could use sodium bisulphate instead, as I do with my reversal bleaches.

Kodak's ECN-2 bleach specifies 10mL/L conc. sulphuric acid.

(10mL) / (98g/mol * 0.98ml/g) = 0.104mol sulphuric acid needed

0.104mol acid * 2mol bisulphate/mol acid * 120g/mol bisulphate= 25g sodium bisulphate.

Could I use this as a substitution? I guess I'd have to test to see if the pH is right. Would the extra sodium and sulphate ions cause any problem? I don't know what the sulphate ions do in this bleach or why acetic acid stop and a sulphite clear couldn't be used instead, but I'd like to find out. Interesting that Kodak doesn't specify a clearing bath even when using a ferricyanide bleach. Clearly the sulphuric acid stop bath is doing something important.

I find it rather frustrating that I can never process a manufacturer's film to their specifications due to not being able to purchase all the chemicals. I try and separate C41/E6 blix kits into separate bleach and fixes using my $15 pH meter which I don't really trust. Part of the reason I thought I would try doing some ECN-2 is because the film is tested with ferricyanide bleach which is much more accessible. I have no confidence that any of my colour films will come out reasonably archivally stable, so my insurance is just to shoot a number of different processes and hope some of them will be OK. I hope to buy a freezer to store my processed colour film someday soon, I imagine that would do some good for stability.

 

[Photo Engineer]

Use the Sulfuric acid if possible!

Glacial acetic might work if at the proper concentration which is NOT the same as H2SO4. Sorry.

PE

 

[Rudeofus]

I don't think Bisulfate is a proper substitute for Sulfuric Acid, just like Sodium Bicarbonate is no substitute for Carbonic Acid, regardless of how much you use. The biggest challenge with Sulfuric Acid is shipment - it appears to be really difficult and expensive to ship a compound which is both liquid AND corrosive.

One compound which is almost as acidic as Sulfuric Acid but comes in powder form is Amidosulfonic Acid (pKa = 1). If this doesn't work out, Oxalic Acid (pKa1 = 1.27) may also work, also comes in powder form and appears to be relatively easy to get.

 

[darkroommike]

Use the Sulfuric acid if possible!

Glacial acetic might work if at the proper concentration which is NOT the same as H2SO4. Sorry.

PE

What PE said!

But if you can not, absolutely can not locally source any type of sulfuric acid, either concentrated or 7N (specified in the formula, or if you don't know what a 7N concentration is) there are more "casual" ECN-2 substitute formulas out there that use Glacial Acetic Acid or even white vinegar(!) at all sorts of dilutions. The official SB-14 pH is 0.8 to 1.5.

 

[iandvaag]

Thanks for the authoritative advice, I really appreciate it. I guess I'll keep looking for sulfuric acid.

 

[mts]

I have found sulfuric acid concentrated in the plumbing department of local hardware stores. Both sulfuric and lye, as well as copper sulfate are used to clean drains and to kill tree roots. However, don't mix them! You can add sulfuric to water to achieve the desired pH. These are no doubt commercial grade but should be adequate for photographic purposes.