You could substitute hydroquinone in the Pyrocat-HD formula. My recollection is that Pat Gainer has actually done it, and so have I. Catechol and hydroquinone work at about the same pH so it would not require a lot of balancing to make it work well.
Originally Posted by olehjalmar
Would it be worth it? Not for me at this point in time since I am very confident that catechol can be used with complete safety in the darkroom.
But others may feel differently.
I guess stranger things have happened, but why is hydroquinone be any less poisonous than catechol? Both have the same empirical formula and differ only in the placement of an OH. The hydroquinone does produce a stain, but of a less versatile color than catechol's. I wouldn't want to sprinkle either one on my salad.
The presence of a visible stain does not always signify a photogrphically valuable stain. The stain has to be proportional to the silver in the image to work its "magic", or you just have the same effect as if you had used a colored gel. There are times when the major part of the stain from one of Sandy's Pyrocat's is so hidden to the eye by the silver image that only printing on both graded and VC papers will show its true extent. Unless you want to bleach away the silver part.
Toxicity depends on a number of factors Patrick. Just as D-sugars and L-sugars differ in activity within the human body, but have the same formula should clue you in to this. Metabolic routes used by otherwise "identical" organic chemicals can cause havoc if used incorrectly.
In fact, the LD of Pyro in Rabbits is much lower than the LD of HQ in Mice even though in humans Pyro is considered odds on to be far more toxic than HQ. In fact, the toxicity of "tanning" developing agents or "staining" developing agents weighed in the exit of Kodak from the Dye Transfer product line from what I understand, but I may be off on this.
There are many other routes to staining developers and tanning developers that involve less toxic routes.
The big difference to my eye in printing pyro negatives with stain is the problem using Azo type papers and the use of UV or visible light. Sandy has alluded to that above. Once you work it out and develop an eye for your negatives things are ok, but before that insight arises, the evaluation of the negatives and printing them is somewhat of a chore if you print conventional negatives a lot.
Last edited by Photo Engineer; 06-14-2009 at 09:31 PM. Click to view previous post history.
Reason: syntax and inversion of data. Sorry all.
How would you relate toxicity to potential for exposure? I mixed up my Pyrocat-HD once back at the beginning of February this year, and will probably have enough developer to last until February next year, so the number of times I'm exposed to Pyrocatechol in dry form is comparatively rather minimal; whereas I might mix up Hydroquinone containing print developers several times a month. In addition, in operational terms I'm only working with a few ml of the developer at a time, wearing gloves, goggles, lab coat etc.
I would not hazard a guess. I had to correct my data above to reflect accurate results. Pyro in tests is LESS toxic to some animals than HQ but is shown to be MORE toxic to humans from what I have read. So, any guess I make would be very off the wall just as anyone else here is.
The considered opinion is that Pyro compounds are more toxic than HQ. I have no more data to back that up than anyone else has to the contrary except the information used by some to say that Pyro is "BAD". Who knows. Use your own judgment and be as safe as possble.
I don't use it, but I have printed from many many Pyro negatives. I find them difficult to print from due to the colored image at the blue end of the spectrum. They offset Azo and MG papers both. To my eye they are difficult to evaluate without a proper filter.
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Yes, I know those things. Ascorbic acid is vitamin C, its mirror image is not, but both work equally well in developers. I just don't know why. If one knows why these things happen, one is more likely to be able to predict when they happen. If we put enough sulfite in a developer, we will not so easilly determine whether hydroquinone of catechol is the regenerator. They both stain when minimum sulfite is used, but the stain is of different color. The dye industry uses many colors that differ little chemically, I think.
Originally Posted by Photo Engineer
I think it is safest to assume that anything we put into a developer is likely to be poisonous. At the same time, if the uses of a dangerous but managable drug in photography are sufficiently desirable, I would not choose agent over another simply on the basis of toxicity, although one I am particularly fond of has nothing but a pinch of Phenidone, a bunch of ascorbic acid, and a wad of borax in it. I used those terms just to tweak your sense of propriety.
All I can speak about is my own experience.
I use PMK extensively, exclusively with traditional films (not t-grain emulsions) although some use it for t-grain films as well. I like the results. I like the tonality. I like how they print.
I like how PMK stock solutions last for years, which is convenient for this occasional worker.
I've used PMK for nearly a decade now and I've no intention of terminating its use, although D-76 and HC-110 do find a place in my darkroom for occasional use.
Jim MacKenzie - Regina, Saskatchewan, Canada
A bunch of Nikons; Feds, Zorkis and a Kiev; Pentax 67-II (inherited from my deceased father-in-law); Bronica SQ-A; and a nice Shen Hao 4x5 field camera with 3 decent lenses that needs to be taken outside more. Oh, and as of mid-2012, one of those bodies we don't talk about here.
Favourite film: do I need to pick only one?
I ain't no stinkin biochemist (so let my ignorance show), but it could be something as simple as what's called "stearic hinderance". Steric hindrance occurs when the size of groups within a molecule prevents chemical reactions that are observed in related smaller molecules.
Originally Posted by gainer
So simply moving on -OH group that is attached to one position on a benzene ring to another may cause geometric effects that either favor or disflavor a particular reaction.
For up from the ashes, up from the ashes, grow the roses of success!
I thought Howard played piano?
Originally Posted by gainer
If the stain is a dye, then surely there must be some sort of post treatment of films to obtain a pyro or catechol like stain for films which have been processed in a non-staining developer if this is desired?
Originally Posted by Photo Engineer