# What's the idea...



## JamesD (Nov 11, 2005)

behind hardening vs nonhardening fixer? I've read that it should be used with film, but not with paper? What gives? The fixer I have, so far as I know, is non-hardening... does this mean that I can't use it to fix film?

Thanks


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## terri (Nov 11, 2005)

A lot depends on what you want to do with your final print. For your negatives, one should always use a fix with hardener to help protect the emulsion from scratches and whatnot. It's always desirable to do this for your film. For paper, it's sort of up to you. 

Will you want to tone your prints, now or later? If you think the answer is yes, use less than the manufacturer's recommendations on the hardener - or, none at all. There are several good books on toning out there, and it seems every author has his own opinion on how much hardener to use, if any. A hardener, as its name applies, will prevent additives from reaching the paper base, which can have a negative impact on the appearance of a toned print. 

I like making bromoil prints, and everything I read on the subject called for plain hypo (sodium thiosulphate), since, in a process similar to toning, the silver is to be bleached out of the print and a hardening agent will prevent that. So I keep sodium thiosulphate crystals around and make my own fix that way, when I am preparing prints exclusively for bromoil printmaking. 

If you have no intention of doing anything further to your prints, a fixer/hardener will protect your print's emulsion. Never a bad idea.  

Again, we shall await the inevitable descent of Mr. Know-it-All into this thread, for additional clarification and edification. :mrgreen:


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## Hertz van Rental (Nov 12, 2005)

terri said:
			
		

> Again, we shall await the inevitable descent of Mr. Know-it-All into this thread, for additional clarification and edification. :mrgreen:


Just for that, I won't. :hertz: 
Terri said it all anyway, so you don't want me throwing chemistry at you.


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## Hertz van Rental (Nov 12, 2005)

Oh go on then.

Gelatine is a protein* and so it's chemistry is very complicated and difficult to understand as there is so much to understand.
Hardening fixers contain chemicals like Boric acid, aluminium potassium sulphate or a chromium compound. They serve as pH buffers but have the added advantage of hardening the gelatine which process aids the drying process and improves mechanical strength and stability.
Gelatine has a microscopic structure that is a bit like a sponge - it absorbs water easily and swells considerably. Hardening it turns the structure into more of a latice that resists swelling and so reduces absorbency. This is why certain post-processing manipulations require you not to harden - you need the emulsion to either swell a lot (Bromoil) or absorb chemicals easier (toning and such).
If you want a more detailed explanation then I will have to start talking about the formation of cross-link bonds between amino acid spines.
Do we really want to go there? :hertz:


I only provide this in-depth technical information because it's like talking dirty to Terri - and we all know a moist Terri is a happy Terri.


*Like egg white, which was used in early emulsions (before gelatine) - albumen prints.


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## terri (Nov 12, 2005)

> I only provide this in-depth technical information because it's like talking dirty to Terri - and we all know a moist Terri is a happy Terri.


 And gooey. :mrgreen: Let's not forget gooey.


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## Hertz van Rental (Nov 12, 2005)

A moist and gooey Terri? I can feel my emulsion hardening as we speak


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## terri (Nov 12, 2005)

Hertz van Rental said:
			
		

> A moist and gooey Terri? I can feel my emulsion hardening as we speak


 And you say chemistry is complicated. :sillysmi:


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## Hertz van Rental (Nov 12, 2005)

It is.
Hardening is supposed to stop swelling but it just isn't working.
I'm going to have to get you into the lab for some tests.


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## terri (Nov 12, 2005)

I will defy such attempts.


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## Hertz van Rental (Nov 12, 2005)

Dang! That means I'll have to send Igor with the mad coachman to get you.
Mad coachmen aren't cheap, you know.






no consideration, some damsels


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## terri (Nov 12, 2005)

But they _can_ be bought....and re-bought, as needed.  


.....JamesD? Why haven't you returned to this thread? We _did_ reply to your query, after all. 



Some people..... :roll:


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## DocFrankenstein (Nov 12, 2005)

:lmao: He probably doesn't want to interrupt. :lmao:

BTT: Hertz - is hardener included in D76 (or D73)... whichever is for film?

You've made me curious as to what bonds are formed. And what structures? Are those alpha helixes or beta plated sheets? Sulfur bonds?


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## Hertz van Rental (Nov 12, 2005)

Gelatine is a protein with a long-chain polypeptide structure - repeating CO2H-CH(R)-NH units. The cross-links are thought to to be formed by ionic bonds between the trivalent ion and carboxylic acid - CO2H - groups of different chains.
Although organic hardeners like Formaldehyde appear to act as 'bridges' and form co-valent (non-ionic) links between the peptide chains.
The info I have is about 25 years out of date and at that time most of it was still guesswork. Don't know if more has been found out yet, but the process for gelatine will be the same as for most proteins. The mechanism in the hardening of gelatine should be pretty much the same as the one in the setting of egg white.
If I get time I'll have a sniff around and see what I can find. If you do it then let me know if you find anything.

PS As far as I know, developers do not contain hardeners - with the possible exception of monobaths.



			
				Terri said:
			
		

> But they _can_ be bought....and re-bought, as needed.


Mad coachmen don't grow on trees, you know. It's not a career move than many people think of making.


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## DocFrankenstein (Nov 12, 2005)

The reason I asked is because I'm studying cell and molectular biology, and since the completion of the human genome project it's all about protein folding.

So every bit of information about protein folding, bonds, crystallization or hardening is of interest.

Ironically, I have no information on either egg white or gelatine.

I doubt if the subject is worthy of the time though. It hardly matters what bonds are being formed in the gelatine, since it will hardly react with anything after the reaction.


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## JamesD (Nov 12, 2005)

Uhmm... should I be frightened? Because I am.

Seriously, though, thanks for the info!


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