How does Hypo Clearing Agent Work? What's the Chemistry?

[mshchem]

I've been using Kodak Hypo Clearing Agent for decades for fiber base papers. Back in the old days of F-5 sodium thiosulfate fixer, the Kodak Darkroom Dataguides put the fear of cold water not removing fixer as a justification for using HCA on everything, including film.

How does it really work? Does it react in someway? Magic? What?

No speculation, I want to hear from a real science person.

Best Regards Mike

 

[takilmaboxer]

Long story short, it reacts with the hypo and makes it more water soluble. Thus, the residual hypo clears faster, especially in fiber based papers.

 

[Sirius Glass]

It works effectively when use as directed. I do not think if is used or needed with FT4 or FT5, but check with Photo Engineer for that.

 

[Photo Engineer]

HCA falls into the category of a wash aid. Wash aids come in two varieties.

One is HCA itself, which is mainly Sodium Sulfite. It is used to force the Hypo out of the coating by displacing it. You then have to displace the HAC with a wash.

The other type sometimes used is based on Hydrogen Peroxide which destroyes residual Hypo.

You can actually use non Iodized table salt. It has the same effect, and that is how this entire procedure was discovered. During the war, navy photo processors used sea water to assist in washing films and prints. The salt in sea water was acting as a wash aid.

Remember that if you use one of these, you have to dispose of this added chemical and you have to wash it out of the coating. Admittedly, the wash is less intense, but nevertheless, it is still required.

PE

 

[Photo Engineer]

It works effectively when use as directed. I do not think if is used or needed with FT4 or FT5, but check with Photo Engineer for that.

HCAs are never required. A good wash does the trick as well. However an HCA can be used at any time with any fixer.

PE

 

[nmp]

I've been using Kodak Hypo Clearing Agent for decades for fiber base papers. Back in the old days of F-5 sodium thiosulfate fixer, the Kodak Darkroom Dataguides put the fear of cold water not removing fixer as a justification for using HCA on everything, including film.

How does it really work? Does it react in someway? Magic? What?

No speculation, I want to hear from a real science person.

Best Regards Mike

Read Richard Knoppow's posts in this thread. Yes, he is a real science person.

https://groups.google.com/forum/#!topic/rec.photo.darkroom/jUo3VYGJQEQ

Key word is ion exchange.

 

[mshchem]

Read Richard Knoppow's posts in this thread. Yes, he is a real science person.

https://groups.google.com/forum/#!topic/rec.photo.darkroom/jUo3VYGJQEQ

Key word is ion exchange.

Later in the post he questions the term ion exchange. If the gelatin is the ion exchange site is he proposing that sulfite exchanges with thiosulfate sulfate? Then the resulting compound is more soluble ???

If I read PE correctly, the strong solution of sodium sulfite displaces some of the thiosulfate (NH4 or Na) from the gelatin. The sodium sulfite is the more easily washed out of the gelatin??. I suspect that Kodak's original selling point, at least it was to me years ago, is that very cold (40°F) water could be used as a final wash after treatment with HCA.

I use KHCA and 70°F water to wash, it's the same workflow I've used for decades and my prints are OK. The Ilford archival procedure relies on HCA, I guess I have faith in Ilford. I will admit I fix longer and wash longer than Ilford recommends .

 

[Paul Howell]

We used HE at our college darkroom in the 60s, I dont think we stopped until 67 or 68 when someone told our lab tech that Kodak had stopped recommending HE. My prints from those days are still in good shape. I use standard Kodak fix for prints followed by Perma Wash, Heico states that double wt prints only need to washed for 10 mins, first wash 5 min, 5 min in Perma Wash, then final 5 min wash. I don't really trust a 5 min final wash and usually wash for 30 mins in an archival print washer washer. I have tested with hypo test after the recommended 10 min wash and my test print tested clear. Still not really sure about such a short wash.

 

[KN4SMF]

I would be interested in hearing the straight poop on Perma Wash. I have always been skeptical on it.

 

[David Brown]

I would be interested in hearing the straight poop on Perma Wash. I have always been skeptical on it.

It contains sodium sulfite. The MSDS is easily found online.

 

[john_s]

Read Richard Knoppow's posts in this thread. Yes, he is a real science person.

https://groups.google.com/forum/#!topic/rec.photo.darkroom/jUo3VYGJQEQ

Key word is ion exchange.

I remember well rec.photo.darkroom. It did deteriorate as it eventually got lots of rubbish posted and there was no administrator. There are gems in there from people like Richard Knoppow who worked a lifetime in film processing (commercial movie film I think). Also Michael Gudzinowicz (I think i've spelled it correctly) was another great contributor. For those that are interested, Richard K wrote a very detailed article on the history of D-76 variants. I could find a link if there's any interest.

 

[Photo Engineer]

Ummm, guys, I am a science guy!

Sorry, just thought a mention might be needed here?

PE

 

[Arklatexian]

Ummm, guys, I am a science guy!

Sorry, just thought a mention might be needed here?

PE

Is a "science guy/gal" a physicist, zoologist, botanist, or maybe even a chemist as they are all "science guys/gals" as are even Photo Engineers. So were the people who wrote the instructions for HCA. Is anyone who looks up the formula for HCA a "science guy/gal.? By the way, I did not realize that "Photo Engineers" had their own Union. However, just to be safe, my motto is, even with HCA, "when in doubt, wash it out". Can't say that I have ever had a print fade in 60 years..................Regards!

 

[Photo Engineer]

I'm a guy who designed processing solutions and coatings for Kodak for 32 years. I'm a guy who has made emulsions and published a book on the subject. That is the one and only reason that I think I have any credibility posting on photo forums.

PE

 

[mshchem]

I'm a guy who designed processing solutions and coatings for Kodak for 32 years. I'm a guy who has made emulsions and published a book on the subject. That is the one and only reason that I think I have any credibility posting on photo forums.

PE

I agree on your expertise. My question is, is there any kind of reaction? I interpret, your earlier statement, that the concentrated solution of sodium sulfite, "displaces" the thiosulfate from the gelatin? The sodium sulfite saturates the gelatin, pushing out a good amount of thiosulfate, ?? Does this make sense?

The mention of ion exchange by Richard K. sounds like a water softener or ion exchange resin.

The posting by Richard K. seems to indicate a chemical reaction? Is this reasonable?

I

 

[KN4SMF]

It contains sodium sulfite. The MSDS is easily found online.

Well if Perma Wash has sulfite as its active ingredient, and the mixing directions call for such a dilute stock solution (which it does), then Perma Wash is every bit the snake oil I always suspected. As I recall, it calls for 3 or 4 ounces or so, of the product in a gallon of water. I am by no means a chemist, but I don't think even the most extreme of supersaturation in manufacturing the product could give a strong enough working-strength solution to do one iota of good. I have always thought Perma Wash was snake oil, although I'd gladly be shown wrong. Because if it was as good as the washing instructions on the bottle infer, then it truly is a miracle product.

 

[reddesert]

It appears that Perma Wash contains more surfactant and less sodium sulfite than hypo clearing agent. Ostensibly, the other ingredients allow it to help get fixer out of the paper.

I used Perma Wash when I was fairly actively processing my own black and white film about 20-25 years ago, I never trusted the idea of the 1-5 minute wash that the bottle says you can get away with, so I washed for, I don't know, 10-20 minutes. Also, I was generally using RC paper, because processing fiber base paper was a PITA (it was the drying that I had the most trouble with). Anyway, my negatives and prints look fine after 20-25 years. I haven't done a residual fixer test, and at this point, not sure I need to.

Maybe they would be fine even without the Perma Wash, but I think in order to call it snake oil, some evidence would be required.

 

[mshchem]

Please, focus on Kodak Hypo Clearing Agent. I don't want to get into a debate about washing aides etc. I'm just curious if there's a good reference on KHCA?

I will defer to PE for his expert advice.

 

[KN4SMF]

It appears that Perma Wash contains more surfactant and less sodium sulfite than hypo clearing agent. Ostensibly, the other ingredients allow it to help get fixer out of the paper.

I used Perma Wash when I was fairly actively processing my own black and white film about 20-25 years ago, I never trusted the idea of the 1-5 minute wash that the bottle says you can get away with, so I washed for, I don't know, 10-20 minutes. Also, I was generally using RC paper, because processing fiber base paper was a PITA (it was the drying that I had the most trouble with). Anyway, my negatives and prints look fine after 20-25 years. I haven't done a residual fixer test, and at this point, not sure I need to.

Maybe they would be fine even without the Perma Wash, but I think in order to call it snake oil, some evidence would be required.

How does one prove a negative? Somehow I tend to put more credence in Eastman Kodak than some third party aftermarket company. What else does Heico make in photographic supplies?

 

[John51]

If the fixer has no hypo in it, eg. Ilford Rapid Fixer, is there any point to using HCA?

 

[removed account4]

You can actually use non Iodized table salt. It has the same effect, and that is how this entire procedure was discovered. During the war, navy photo processors used sea water to assist in washing films and prints. The salt in sea water was acting as a wash aid.

Hi PE
it was my understanding ( maybe I understand wrong ) that the sea water the navy used to speed up the process contained a lot of other stuff
( like most seawater ) and some of that "other stuff" was sodium sulfite and it was after studing that sort of stuff that EK and others invented fixer remover.

I'm a guy who designed processing solutions and coatings for Kodak for 32 years. I'm a guy who has made emulsions and published a book on the subject. That is the one and only reason that I think I have any credibility posting on photo forums.

PE

Sure DO ! Its nice to remind the new-b's

your background though

How does one prove a negative? Somehow I tend to put more credence in Eastman Kodak than some third party aftermarket company. What else does Heico make in photographic supplies?

Heico has been making Perma Wash for a long long long time they are not an aftermarket company. Its like suggesting that Ilford is an aftermarket company because they don't make Kodak Chemistry. I've used perma wash since IDK 1988 seems to work fine, also have used sprint fixer remover, which works great too. I've also done tests on my prints and negatives to see if there is residual fixer in there, after using Perma Wash and there isn't. And when I submit work to state and federal archives where the negatives and prints are routinely tested for residual chemicals, they come out clean too.
YMMV

I might be wrong but I think with photography because there are so many variables that can screw everyting up, the trick is to figure out what works for you and just do it ... no matter if it is Kodak, Champion, Ilford or Heico or Sprint. A lot of the chemistry is pretty straight forward its just their proprietary additives that might give them the edge like the detergents and anti oxidents in gasole, hair care products, spices in food, or laundry detergent..
If you don't get a rash and your clothes are clean, rinse later repeat..

Here's an ad for the rest of the photochemistry they make/made

 

[Rudeofus]

Here is the scientific foundation of HCA (see PDF attachment).

Short summary of attached article:

1. as freshly fixed film is washed, initially thiosulfate washes out very quickly.
2. some thiosulfate stays attached to gelatin matrix and is very slow and difficult to wash out.
3. several anions (chloride, carbonate, sulfite) are known to engage in an ion exchange process with the thiosulfate trapped in the gelatin, with sulfite being the best of them.
4. as the charts in Figure 1 imply, even very low concentrations of active compound are sufficient to make a working HCA.

 

[Photo Engineer]

Ok, another thread like the one on Stop Bath use I guess.

Any wash aid is better with FB papers than it is with RC papers. That said, it does help with the emulsion itself to a tiny amount.

Emulsions are like ion exchange resins. In fact, they resemble a mixed bed resin, having both positive and negative charges. Gelatin, or rather the amino acids it is made of, likes to hold on to both positive and negative ions. It also likes to surround them with its coils and "embrace" them. Thiosulfate is a big negative ion, having both Sulfur and Oxygen bound together with a double negative charge. It is held on tightly. Complexed with Silver it is bigger and more tightly bound. In fact there are at least 5 different complexes of Silver with Thiosulfate and some of these are very huge.

What you need to do is remove them by water, and lots of it, or with a big dose of an ion, or to destroy the hypo itself. Paper holds onto this as well. The sizing agents that make paper work, are also liable to hold on to Hypo. HCA is a big dose of ions. It is like washing out an ion exchange resin with an inert salt. Thus, any inert salt will work. HCA uses Sulfite. Seawater would work, but I am not aware of any Sulfite present, just the usual mix of Halides. That is why regular salt will work.

Thus you have the sale of a rather inert chemical to remove Hypo when water would do the trick. You have more chemistry to dispose of, one way or another, and you still have to wash the film or paper to get rid of the HCA. Now, there is a test for residual Silver and residual Hypo, but none for residual HCA!

There is a simplified explanation of HCA. As to using it? I never have. I have had no problems in all of my years except for pictures made when I was about 8 years old. I did not wash enough. Of course back then, I had to be reminded to wash behind my ears.

And thank you John.

PE

 

[mshchem]

Here is the scientific foundation of HCA (see PDF attachment).

Short summary of attached article:

1. as freshly fixed film is washed, initially thiosulfate washes out very quickly.
2. some thiosulfate stays attached to gelatin matrix and is very slow and difficult to wash out.
3. several anions (chloride, carbonate, sulfite) are known to engage in an ion exchange process with the thiosulfate trapped in the gelatin, with sulfite being the best of them.
4. as the charts in Figure 1 imply, even very low concentrations of active compound are sufficient to make a working HCA.

Thanks!

 

[mshchem]

Ok, another thread like the one on Stop Bath use I guess.

Any wash aid is better with FB papers than it is with RC papers. That said, it does help with the emulsion itself to a tiny amount.

Emulsions are like ion exchange resins. In fact, they resemble a mixed bed resin, having both positive and negative charges. Gelatin, or rather the amino acids it is made of, likes to hold on to both positive and negative ions. It also likes to surround them with its coils and "embrace" them. Thiosulfate is a big negative ion, having both Sulfur and Oxygen bound together with a double negative charge. It is held on tightly. Complexed with Silver it is bigger and more tightly bound. In fact there are at least 5 different complexes of Silver with Thiosulfate and some of these are very huge.

What you need to do is remove them by water, and lots of it, or with a big dose of an ion, or to destroy the hypo itself. Paper holds onto this as well. The sizing agents that make paper work, are also liable to hold on to Hypo. HCA is a big dose of ions. It is like washing out an ion exchange resin with an inert salt. Thus, any inert salt will work. HCA uses Sulfite. Seawater would work, but I am not aware of any Sulfite present, just the usual mix of Halides. That is why regular salt will work.

Thus you have the sale of a rather inert chemical to remove Hypo when water would do the trick. You have more chemistry to dispose of, one way or another, and you still have to wash the film or paper to get rid of the HCA. Now, there is a test for residual Silver and residual Hypo, but none for residual HCA!

There is a simplified explanation of HCA. As to using it? I never have. I have had no problems in all of my years except for pictures made when I was about 8 years old. I did not wash enough. Of course back then, I had to be reminded to wash behind my ears.

And thank you John.

PE

Thanks!