"Safe" Replacement for Formaldehyde Pre-Hardener?
I am working with some greatly expired (1970's) color negative aerial film, and have been told by the helpful folks at Kodak that the film requires a formaldehyde-based pre-hardener, as well as a formaldehyde-based dye stabilizer during the developing process, with these chemicals being discontinued 10-15 years ago due to toxicity concerns.
I did a series of clip tests of the film using black-and-white chemistry, and found that at too warm of temperatures, the emulsion became so soft that it bubbled and sogged off of the film base entirely. I was able to keep it all together by doing a "cold" develop (just a touch above room temperature) with very minimal agitation, but I still experienced some reticulation in the end. However, all told, I found the film to produce an image which was usable enough for my purposes.
The questions I have going forward:
* Is there a reasonable (less toxic) substitute available as a formaldehyde-free pre-hardener? Note that I'm not interested in a formula to re-create Kodak's discontinued chemistry.. I'm looking for something that is safer, even if it is less effective.
* Should a hardening fixer be used with film of this type, or was it intended that all of the hardening be done prior to the developer?
* In the absence of a suitable pre-hardener, are there any other chemicals or process changes which would minimize the swelling of the emulsion or the chances of reticulation?
Thanks for the help.
Last edited by Scheimpflug; 08-15-2011 at 06:00 PM. Click to view previous post history.
The purpose of a formaldehyde hardener is to create cross-linkages in the emulsion. These cross-linkages harden the gelatine and make it less soluble. Formaldehyde has the disadventage of being a gas and is released from aqueous solutions. A higher molecular weight aldehyde like glutaraldehyde or succinaldehyde could be substituted. These would remain the water solution. A 10% solution of glutaraldehyde is sold under the name Diswart and is used for wart removal. Commercially glutarladehyde is sold as a 50% solution.
There has been a concern about long term or chronic exposure to formaldehyde. Short term exposure is another matter. While it is irritating to mucous membranes and the eyes there appears to be no lasting effects from dilute solutions. It has been used in embalming solutions for more than a century. If it were as toxic as some would make it then morticians and medical students would never survive their exposure and live into old age.
A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.
~Antoine de Saint-Exupery
Formalin has two purposes in these films.
1. Cross link the gelatin and harden it as Jerry says.
2. Stabilize the dye images by reacting with the excess coupler to form a "neutral" environment for keeping.
Pre hardener formula:
Sodium Sulfate 100 g/l
Formalin 3 - 10 ml /l
Sodium Carbonate 10 - 50 g
pH 9.0 - 9.5
Treat for 1 - 5 mins at the working temp then wash 3 - 5 mins.
Make up Photo Flo 200 at the working strength as on the bottle.
Add 3 - 10 ml of Formalin to 1 L of this.
Use for 1 - 2 mins at the working temp.
There is NO substitute for Formalin (37% Formaldehyde gas in water) for these purposes).
Thanks for the replies.
Do you happen to know the shelf life of a mixture of the pre-hardener? (Is it something that you could make a liter of it and keep for a while, or would you have to keep mixing the Formalin-3 each time you use it?)
Also, assuming that you can make the film survive the development without the pre-hardener, and assuming you are developing just the silver layers of the color film with B&W chemicals, am I correct that a Formalin-based dye stabilizer would not be needed? In this case, would a hardening fixer be enough to make the film less delicate when it is done being developed?
In the pre hardener the sulfate and carbonates are inorganics. They are stable. The formalin inherently resists organic degradation. Yes, the pre hardener is reusable; it may discolour as any film overcoat partially dissolves in it as it acts; I would not worry about that.
Keep in a well sealed nearly full bottle to keep the gas in the solution. I'm still at about 970ml of a litre of formalin (saturated solution of 37% formaldehyde) I bought over 5years ago. Once I get to where there ia a larger gas space in the bottle, I may elect to add marbles to decrease the volume of air for the formadehyde to off gas into.
my real name, imagine that.
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The formalin final rinse prevents dye problems (I think it relates to the stability of the colour couplers ) in the older generation of colur films you are playing with.
So yes, a formalin rinal rinse is still recommended even if you squeeak through keeping the unhardended emulsion on the base by doing low temperature processing.
my real name, imagine that.
The Formalin "3" is meant to be read as a range of Formalin from 3 ml/l to 10 ml/l, and that is all.
As Mike said, the prehardener will discolor due to the added dyes in films. I am not sure if the film will survive without the prehardener, but if it does, it surely will need either a hardening stop, a hardening fix or a plain hardener bath. At that time, some color processes used a chrome alum hardening bath.
For other soft emulsion film, like Efke, could formalin be added to the developer to harden the emulsion?
Now that I have your attention, there are some cases you can do either or both. Some lith developers use formalin and some non-ammonia fixers use formalin. In these cases, remember that any amines or ammonia present will react with Formalin, so Metol will react as will a PPD developer. Ethanol Amine and Diethanol Amine will react with Formalin. Ammonium Hypo will as well.
If you are going to play with this, you have to know some chemistry.
You seem pretty adamant about that!
So obviously it should in an independant hardening bath to be easy and without risk.