Denise cadmium turns the image tone towards green Potassium towards brown at least according to older sources. Never used cadmium as it is extremely difficult to get in Austria.
I imagine few emulsion makers will consider using cadmium given its extreme toxicity for minimal reward. I actually have a bottle of it, but I think I'll finally get around to disposing of it when the local sanitation company has its next HazMat collection day.
None the less, the discussion is interesting from a historic perspective. I dug through Glafkides (Photographic Chemistry, Vol 1, 1957) this morning.
"Cadmium is a retarder of physical ripening. Its action with chloride emulsions results in an increase in contrast. The addition of cadmium salts is made before precipitation." p.318.
Gladkides then goes on to spell out a number of chloride emulsions with increasing levels of cadmium. An "Extra hard unwashed chlorobromide emulsion" has 80 g NaCl, 20 g KBr, and 40 g of cadmium chloride for 200 g of silver nitrate. (It also has sulfuric acid, egg albumen, and "color sensitizer".) It's the kind of recipe that gets geeky hearts all in a twitter. But, I think, best to leave that one safely on the page -- not running loose in the home darkroom.
The best Papers for Lith also had cadmium in them after the cadmium ban by the EU a lot of great lith papers merely became good Lith paper. We're talking image tone and to some extent quality of grain. Also some people believe that cadmium was a better emulsion preserver than what is now in use.
I wouldn't throw away the cadmium some of the best paints were also cadmium based and the lack of cadmium (yellow, red,...) resulted in a severe loss of quality at least according to some painters and conservators I know. Same applies to lead white which is vastly superior to other white pigments but again contains an evil ingredient lead. I wonder if lead bromide was used in emulsions as well
The only information I can find about lead is again in Glafkides. p.318.
"Lead and thallium reduce sensitivity and increase fog. Thallium was disclosed by Schwarz in 1926. Mueller stated in 1935 that lead and thallium salts added in a concentration on 0.04 molecules per cent of the silver halide increase the sensitivity of gold-sensitized X-ray emulsions of 50-100%. The addition is preferably made before precipitation."
re lith paper: At one time, I thought lith printers would be a natural cohort of d.i.y. emulsion makers. If I were a lith printer, I'd definitely keep and use my cadmium. But, I think I won't be R&D'ing many new emulsion recipes just for the sake of R&D. There just isn't the interest to justify the time. (Fortunately, it hasn't been expensive research!) Time for this girl to leave her lab-rat comfort zone and get back out into the world and try to "make good art." There really is a ridiculous amount of how-to information on the Light Farm already. It's good info and you can't beat the price!
The problem with cadmium is that it's near impossible to get it in the EU and so are a lot of other products necessary for the production of serious emulsions
Under the guise of safety and environment the EU is very anti chemistry and homebuild products (safety and environment my behind) In Austria I can't even get chromium alum.
These sad facts are imo the main cause for the lack of interest in emulsion making in Europe we all like to do it but we can't. Aside from very simple emulsions that is.
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In all honesty, I don't know the definition of "serious emulsion". Every chemical I've used for my daily photography for the last six years is available in the EU.
Not so long ago, simple emulsions (and just making them stick to a glass plate, for gawd's sake) seemed like a great goal here, worthy of long discussions. Maybe it's my fault that has changed. I pushed the envelope each time I heard 'impossible'. I have pushed back against the idea that nothing can be learned from the old literature. Simple equipment? Faster than ASA 40? Handheld shooting? Roll film? Ortho film with affordable, available dyes? Panchromatic film? Each and every earned a loud 'Bah! Humbug!' until I did it, and then the goal bar ratcheted up. It has finally reached the place that anything made in a home darkroom is inferior just because it wasn't made and tested with equipment that is truly out of reach of almost anyone. Also, some of the assertions of fact I've read here are nothing of the sort. Not quite sure why the nonsense is even paid attention, but if there's anything the last couple of weeks of US politics has taught us -- people are going to believe what they believe -- facts be damned.
Anyway, I do think that more and more people will be making handmade objects in the years to come. When anything and everything can be bought at Walmart or made with a 3D printer, the hand-sewn, hand-woven, hand-painted, hand-carved, hand-blown, and hand-printed will be precious and valued again. In the meantime, those of us who have never believed otherwise (and we are many) are having a great time!
Denise the term serious was not meant as derogatory and was a misuse of the word I should have said simple like Kevin Klein's superb emulsion and something a bit less simple like your emulsions the Glyoxal btw is already less easy to get in Austria and Osterman's emulsion contains chrome alum so is pretty much impossible to do in Austria and to some extent in Germany.
I think we are just in a down cycle right now regarding emulsion making. It's just the wrong time of the year for me. There is definitely some of the "bah, humbug" for the "required" perfection level but I really could not care. Anything I've made and tried to reproduce, I can reproduce at the level of my grandmother's chocolate chip cookies - I knew pretty much what they would be but no they weren't precisely the same every batch. Big deal. It's all good.
Another thing is that I think many makers get discouraged that they cannot get past ISO 40 or 50 and give up. Or they do get past that speed and maybe go off into some secret laboratory. Who knows? One of us will find the secret to ISO 100, 200 and maybe even 400 for the home based worker. Then again, what's wrong with ISO 50 anyway? Many here would kill for Kodachrome 64.
Now as far as cadmium, its up to you of course, but cadmium was used for a long time before it was deemed evil. We used cadmium plated hardware at work until just a few years ago when it was banned. (Don't know exactly how much cadmium was used in that stuff, though.) I don't doubt that it's toxic but we would probably use very little at any time and you aren't supposed to eat the stuff! Use the necessary precautions and I am sure it is fine. Many other substances are the same.
The company I work at does a good bit of business in the EU. The restrictions placed on EU things are disappointing. I don't pretend to understand what they are doing but it seems over restrictive to me and stifling to industry and innovation.
All this has happened before, and all this will happen again.
Both of you make excellent points. I very much respect and appreciate your feedback. The immediate take-home for me is that I need to edit TLF to include a condensed, heavily annotated "edition" that addresses the concerns and needs of people in the EU. I thought that the tutorials did that. There aren't any recipes there that include chrome alum, or anything but simple ingredients. But, admittedly, there is an awful lot of information. It's kinda been my thought that interested and motivated folk would dig into things and understand the doability of home emulsion making. That may be a lot to expect. I know that I gave up on an excellent website on handmade paper. Too much for brain to absorb!
I will give serious thought to a re-write, but I'm deep and happily into my personal art goal of color photography right now and need to decide how selfish I want to be with my time.
Indulge one more toot of my own horn. I make (and it is not hard) ASA 100 film. That's its speed in full summer light. It's a bit slower than that in the shade or in the winter. All the images on these pages were shot handheld. 120 film. Note the stop-action of some pretty fast-paced movement.
It was my intention to get this recipe onto the tutorials, but I'm holding off because of the issues raised in this thread and the one I started about emulsion making. I have matched up the recipe with an enlarging paper. It's a pretty nifty combo, and hopefully there will be an audience for it someday. The Light Farm is all about community and cooperation, and learning from feedback. I know I don't have all (or even most!) of the answers. All I know is my commitment to handmade silver gelatin emulsions. I hope the conversation will continue.
It is important to distinguish between a chemical used as a source of bromide ions and a bromide containing various heavy metal cations. These latter chemicals are used for a purpose other than mere precipitation of silver bromide. Their discussion veers away from the question in the original post.
Last edited by Gerald C Koch; 10-17-2013 at 11:47 AM. Click to view previous post history.
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