Metol, hydrolysis

Raghu Kuvempunagar · May 12, 2021

michael_r said:
Perhaps you guys have inadvertently stumbled into the reason why most iterations of Kodak HC-110 contain a small amount of catechol.

Possible. But there's a small difference. HC-110 concentrate has no water in it. So the catechol in it could be primarily to extend the life of working solution. In contrast, Edwards 20X concentrate is water based. So Catechol could be extending the life of both concentrate and working solution in its case.

relistan · May 12, 2021

Raghu Kuvempunagar said:
Is Ascorbic Acid not superadditive with Catechol? I see the pair being listed as superadditive in some threads in this forum. Not sure I saw anything on this pair in Haist.

Hast definitely doesn't list it, I looked. He doesn't actually talk about ascorbic acid all that much. In the late 70's it was not a common agent.

I had seen ascorbic acid mentioned with catechol but thought maybe it was to do with its other properties as a preservative.

relistan · May 12, 2021

Raghu Kuvempunagar said:
Possible. But there's a small difference. HC-110 concentrate has no water in it. So the catechol in it could be primarily to extend the life of working solution. In contrast, Edwards 20X concentrate is water based. So Catechol could be extending the life of both concentrate and working solution in its case.

Correct me if I'm wrong but wasn't HC-110 originally formulated for bulk processing where the working solution life was super important?

Raghu Kuvempunagar · May 12, 2021

relistan said:
Hast definitely doesn't list it, I looked. He doesn't actually talk about ascorbic acid all that much. In the late 70's it was not a common agent.

I had seen ascorbic acid mentioned with catechol but thought maybe it was to do with its other properties as a preservative.

Here's a post that lists Catechol and Ascorbic Acid as a superadditive pair.

Alan Johnson · May 12, 2021

On my Pourbaix diagram Ascorbate has E (SHE) around pH 7 =0.2 and at pH13 = 0.0.
This puts it below hydroquinone. If it is speculated that catechol will give lines similar to HQ then ascorbate will fall below catechol.
In theory ascorbate could reduce catechol.

https://www.photrio.com/forum/threa...what-have-you-made.180840/page-3#post-2371337
diagrams -posts 43, 53.

Pixophrenic · May 12, 2021

Raghu Kuvempunagar said:
Here's a post that lists Catechol and Ascorbic Acid as a superadditive pair.

This post you reference just lists available pairings. It does imply but shows no proof they are all superadditive. Adding a little metol to speed up a developer does not conform to the definition of superadditivity. In case of catechol and pyrogallol this is complicated by the production of stain, which makes many people think that these form superadditive combinations in low sulfite compositions.

MattKing · May 12, 2021

relistan said:
Correct me if I'm wrong but wasn't HC-110 originally formulated for bulk processing where the working solution life was super important?

Usually though in a replenishment regime.

Lachlan Young · May 12, 2021

michael_r said:
Perhaps you guys have inadvertently stumbled into the reason why most iterations of Kodak HC-110 contain a small amount of catechol.

It may be acting as a scavenger - or as some form of anti-dichroic stain agent (as per the tiny amount of chlororesorcinol in Microdol-X) - and given that HC-110 was supposed to be replenishable down to 1+47 or so, I wouldn't be massively surprised if it had to do with something more specific in terms of deep tank/ replenished use than acting as a developing agent assist.

Metol, hydrolysis

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