Spice-rack alum as film hardener?

[joe_k.]

I know this isn't an auspicious start here on Photo.net, but I *do*

have some darkroom experience... just enough to allow me to have these

crazy thoughts.

 

So... theoretically speaking, would plain old McCormick Alum

(potassium aluminum sulfate, as far as I can tell) suffice as a film

hardener? If it might, would it be safe and sane to add it to stop

bath, or would this risk incomplete fixing if it actually works?

 

How about a 'standalone' solution in water or distilled white vinegar,

as a pour-in/pour-out after the first stage of an Ilford-style rinse?

[jimvanson]

Joe -- For a start, why are you using hardener?

[discpad]

You need it with Efke and Foma films, since they have very soft emulsions which scratch easily. :(

[joe_k.]

Well, as noted two posts down, we'll be processing some Neopan SS for scanning, which is likely to be mildly abusive to the emulsion side... and we'll be using Paterson AcuFix, which is "non-hardening" but does contain an "anti-swell" agent, so the literature goes.

 

Opinions on SS's durability vary, and I always used to add the hardener to my Kodak Rapid-Fix for not "knowing better" (shooting the more modern Presto 400, then), so it'd be neat to know if there's already a 'solution' in the cabinet if fragility actually proves a problem. (Especially while the film is still wet, since it'll be squeegeed by fingers with rough skin or long fingernails, respectively. ;))

[lex_jenkins]

I've used ordinary kitchen grade alum when experimenting with sizing homemade papers, sketch pad papers or various watercolor papers after the original sizing has been scrubbed out in spots from overworking certain areas.

 

Some sources say alum is not best for archival use. There are other hardeners available. You could probably find 'em researching Kodak's and art paper websites.

[rowland_mowrey]

Clay, which contains a lot of aluminum salts is used to size papers, even those used in photography. It 'hardens' cellulose and makes it stick together to make paper.

 

Surprise surprise!

 

Anyhow, I doubt if aluminum salts would have a severe effect on paper image stability.

 

Ron Mowrey

[joe_k.]

Okay, if I'm up late reading, let me add to this -- hardener before fixer in general: good idea, bad idea? I read that hardening stop used to exist for film use, and if I 'have' to try this, it'd save a bottle and provide an acidic environment... While, in turn, a separate jar of pickle juice isn't too hard to store if it'd be a much better idea to try after the majority of the hypo is out. (So I already know better, but it sure would be convenient to save a jug and a step, if results would be on par with how this emulsion was probably treated when it was new... and this is all "in theory," anyway.)

 

What's a usual soak time for 'real' standalone film hardener?

[larry_kalajainen2]

With most modern films (possible exception the Efke and Foma, since I know nothing about them) don't need a hardener and are fairly scratch-resistant. I haven't found scanning images to be injurious to the film if you're reasonably careful.

 

Hardener in any form will add significantly to your final wash times.

Best to just forget it.

[don_mckeith]

Subject: Response to Spice-rack alum as film hardener?

 

since I have shot a fair amount of Efke 25 and 100 and Jand C classic 200(I forget which film this is) in both 120 and 35mm, and have suffered my share of scratches,

I'll add my $.02

 

imo, most scratches are caused in camera, or loading the film onto reels-in which case alum ain't gonna help

[joe_k.]

Heh, quite agreed. Of course, *my particular situation* raises concerns about scratching during the squeegeeing, and abrasion dragging the dried emulsion against a contacting scanner bed (this particular model has a filmstrip-size backlight holder device, which Microtek calls a 'Lightlid 35;' if you see how it's used in practice, there's enough opportunity to scrape both inserting the film, or grinding it against the scanner bed while positioning, especially if you're doing fine adjustment to get things perpendicular)... But at this point, I'll just report back if we end up risking it, and introduce it *after* the first rinse post-fixer, if so. If anyone else gets crazy enough to add it to stop, let me know. :)

 

Thanks for the thoughts!

[don_mckeith]

Joe-

 

I read a post(Ithink on this forum) by someone who seemed to know what he was talking about,who stated that alum was only effective during wet processing,and once the film was dry it would have the same hardness,weather or not some kind of hardener was used.

 

 

this makes sense to me because what alum does is reduce swelling in the emulsion,which is a non issue when the film is dry-

 

but I'm no chemist

 

I did a search but couldn't find it-will try again,when I have some time

[rowland_mowrey]

Guys;

 

Alum (Aluminum Sulfate) hardens by two methods. Sulfate ion in solution decreases swell of gelatin. Aluminum, being trivalent, forms ionic bonds with amino acids. As a side note here, alum is less effective if your coating is very swollen to start with. The aluminum bonding has a limited 'reach' and becomes more effective if the gelatin swell is reduced. An acid stop bath helps the alum harden, but a water rinse after the developer does not.

 

These two 'reactions' are reversed by alkali and by the wash due to the copious water removing the bulk of both the aluminum and the sulfate.

 

Traditional true hardeners such as formaldehyde etc. form covalent (permanent) bonds with the amino acids and irreversably harden the film. They can also reduce swell by chemically pulling the amino acids closer together by means of this true bond. Washing will not remove this bond.

 

Strong alkali will reverse or remove any hardening in a gelatin as long as it is strong enough, treatment long enough, or hot enough. Hardening works by means of raising the melting point of gelatin through bonding (ionic or covalent).

 

Gelatin swelling is minimized at the isoelectric (neutral) point of the gelatin. For normal gelatin, this is about pH 4.5. Therefore, the sweet spot is at that pH for minimizing swell and scratching. But, there is a tradeoff with swell and fix or wash efficiency. As swell goes down, the 'pores' in gelatin become smaller, and restrict the diffusion of fix chemistry into and out of the gelatin thereby requiring increased fix and wash times.

 

The best compromise, as I have been trying to explain in other posts, is a fix with a pH of about 6.5. It is a compromise between the extremes of acid and base fixes for speed of fixing, swell, and wash times.

 

Gelatin swell is measured with a swellometer in microns, and hardness is measured with an abradometer which measures scratchability in terms of grams of pressure. The pH of gelatin in a coating is measured by means of a surface pH electrode. All of this is very expensive specialized equipment used by EK and other mfgrs to test films for hardness.

 

I have simplified this a lot. Photographic chemistry and engineering is a very large and complicated field. We only touch the surface in these discussions. There are a lot of proprietary methods and a lot of art used as well as what I mention here.

 

Ron Mowrey

[joe_k.]

Awesome -- I give up, and get a great answer. Thanks, Ron!<BR><BR>

 

<i>The aluminum bonding has a limited 'reach' and becomes more effective if the gelatin swell is reduced. An acid stop bath helps the alum harden, but a water rinse after the developer does not.</i><BR><BR>

 

So an acidic solution would be required for it to work at all, as I came to guess...<BR><BR>

 

<i>These two 'reactions' are reversed by alkali <b>and by the wash</b> due to the copious water removing the bulk of both the aluminum and the sulfate.</i><BR><BR>

 

...but it'll all go back into solution if the film is washed thoroughly, making it most useful as a temporary anti-swell agent... and the pH 5-6 (IIRC) Paterson fixer already has one... which just might be alum anyway.<BR><BR>

 

I think you've just saved me a lot of putzing around, and explained why the 'real thing' is necessary if you want the real thing. :)

[don_mckeith]

like I said-

 

someone that seems to know what he's talking about-

 

the chemists come out of the shadows

[rowland_mowrey]

As I remarked earlier, Alum is precipitated by alkali and loses effectiveness. It forms a white scum on the surface of and within the film or paper it is being used with. It partially washes out in water and can be removed by treatment with acid. Therefore, use of an alum hardener after the developer without a stop or without any treatment at all can cause problems. A wash is better than nothing at all.

 

This scum is aluminum hydroxide. Aluminum is what is called an amphoteric element. It is affected by and reacts with both acids and bases. That is a simplified explanation.

 

Ron Mowrey

[don_mckeith]

Rowland-

 

can aluminim sulfate or chromate make a gelatin emulsion harder than it started out to be(after it is dry), under any circumstances?

 

 

extra credit- I have a glass plate albumen formula that calls for

35g. silver nitrate + 5ml acetic acid in 12oz distilled water-

 

would you guess that they mean 98% acetic acid or 28%- or does it matter?

 

TIA

[rowland_mowrey]

Don;

 

I studied Aluminum, Zinc, and Zirconium hardeners, but not Chromium. All of these that I studied generally were not permanent or rather had their effects diluted during the wash after the fix. Zirconium was the odd one, giving case hardening or what amounted to hardening of only the surface of the film or paper.

 

Chromium hardeners were a no-no due to toxicicty and environmental problems from chromium ion. In fact, Zirconium (zircotan) was also eventually forbidden. Oh, BTW, Zircotans name comes from the 'tanning' or surface effect that it gives.

 

Anyhow, all I feel competent to comment on are the Alum and Zinc hardners and a little on Zirconium.

 

As for your acetic acid question, I have no idea, but I would guess it is probably concentrated Acetic Acid, but OTOH, if the acid is too strong it can denature the gelatin and cause it to turn into clumps. The way to test it is to try it I would guess. Remember, the silver nitrate is a very srong acid itself. Your sign of failure will be the formation of a gluey white glop in your container as you add the silver nitrate / acid solution.

 

Sorry I cannot be more helpful.

 

Ron Mowrey

[don_mckeith]

Thank You ,Ron

 

very informative