Hardening v non-hardening fixer (Kodak Unifix)

Discussion in 'Black and White' started by giverin, Nov 19, 2010.

  1. I bought some photographic paper locally from a guy who was giving up his darkroom and getting rid of all his equipment. He kindly let me have a lot of stuff that he couldn't be bothered to advertise, things like tanks, reels, clips and contrast filters. He also gave me a load of fixer. A 5 litre bottle of Ilford Hypam (which is the fixer I normally use) and a 5 litre bottle of Kodak Unifix, which I had never heard of.
    A bit of research shows that this is a hardening fixer. I'm still a bit of a novice and I don't really understand the difference. I know that most rapid fixer is non hardening. I assume that hardening fixer makes the negative less likely to damage and I assume the downside is a longer fixing time? What about using a hardening fixer for fixing prints? I would like to make use of this Kodak stuff if possible. I'm assuming that shelf life isn't too much of an issue for fixer if still in concentrate form?
  2. You're right. It does make the neg tougher but fixing and washing times increase. I've never used hardening fixer because most modern films are tough enough. That said, some emulsions are rather fragile and might benefit from a hardener. I use Ilford films almost exclusively, except for the odd roll of Fuji or Kodak, and I have never found the need to use a hardener.
  3. You can of course use this for prints, however, if you plan to tone them it creates problems.
  4. You can use the hardening fixer with no problem. I used one for many years and never had a problem with it. I still keep some around for the occasional times when I might need it. The only real consideration is that your final wash times will be longer. What Ann says about toning prints is true. My observations indicate that the toning process takes longer and the color may be different than what you'd get had you used a non-hardening fixer.
  5. I use the Photographer's Formulary Archival Fixer, and it too is non-hardening. Seems to work fine although I, like you, worry about whether to use a hardener or not, just a little. I'm just careful in handling the negatives, and as soon as they are dry the negatives go directly to the scanner.
  6. The term fix mean to render permanent thus we call this solution a fixer. Fixers use one of two chemicals fix agents. Sodium thiosulfate and ammonium thiosulfate called "hypo" in the photographic vernacular. Ammonium thiosulfate works faster so its nickname is rapid fix.
    Now films and paper consist of a layer of highly purified gelatin coated onto the base support, be it film or paper. This is the glue or binder for the light sensitive salts of silver that make chemical photography possible. No substitute for gelatin has ever been discovered. Gelatin is derived from animal bone and skin. Gelatin replaced egg whites thus relieving the labors of millions and millions of chickens.
    Gelatin is used because it is transparent, flexible, has low solubility, reacts to boost ISO, but most of all, has a structure swells when wet allowing fluids to freely circulate. This structure allows entry to the chemicals of developing. When the material dries, the gelatin shrinks almost to its original dimensions. When wet and swollen, the gelatin is particularly vulnerable to damage by scratch, abrasion, or separation. Keep in mind, manual and automated can be a bit forceful. The potential damage is greater if the process is carried out at elevated temperatures.
    Many films and papers are pre-hardened to allow them to tolerate some abuse. A hardening agent is often added to the fixer to bolster the robustness of film and paper. Potassium alum is often the hardener as it also a antisludging agent plus it buffers the pH. Chrome alm is preferred if the temperature of the process is high.
  7. if i remember correctly, Nelson's gold toner recommended a re-fix after toning with a fixer with hardner, and so we also kept some around the lab for just this purpose.
  8. Thanks to everyone for their helpful replies.
  9. My question - and Ann you may have indirectly answered it, is can I use hardening and non hardening on the same
    sheet? I want to use up the last of my kodafix as a first fixer bath but start switching to nonhardening and use it as my
    second fixer bath (only while the kodafix is still good)

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