Potassium cyanide fixer

mattmoy_2000 · Jun 9, 2010

PLEASE don't use this. I handle KCN (both the salt and in aqueous solution) at work in a lab and the safety precautions we have to take are immense. The quantity of cyanide you're talking about using is enough to kill 10 large men.
The LD50 of KCN is about 6mg/kg. It's not worth the risk. Death occurs within minutes, and it's not pleasant from what I've read (not a great way to kill yourself, accidentally or deliberately).
If you do insist on using it, it's denatured by bleach, so have a large quantity of that to hand and soak everything that might be contaminated with KCN or KCN(aq) in it for at least 2 days. It produces some sort of gas and is very exothermic. I don't really want to know what the gas is. (Sodium hyposulphite, I believe is what we use in the labs - I'll have to check, which is a primary ingredient of... oh yeah, NORMAL fixer!). Wear thick rubber gloves, with latex gloves underneath to enable safe degloving and use in a well ventilated place, preferably a fume cupboard. Wear face protection (e.g. a welding mask) and make sure you always have a second person present when you are using it. Do not even think of having it anywhere near acid, and do not store aqueous solution- it degrades to HCN when in solution, which is a lot more likely to kill you, since you might breathe it in inadvertently.

To put this bluntly, Potassium Cyanide is really not something you want to frick around with, and which should be avoided if at all possible.

Sorry if I appear patronising, but I handle the stuff fairly regularly and it scares the sh*t out of me and all my colleagues when we have to handle it.

Cor · Jun 10, 2010

Ok,

Now my part: the use of KCN is a hot topic in the Wet Plate Collodion world. I'll just tell my way of working (BTW I work in a lab and thus have easy access to good safety equipment such as a flow hood etc.).

I make a 1% stock of KCN, thus far I have made 1 batch of 1 liter, in which I have at least ran 70 or so whole plates through. So advantage one is the high capacity.

Working inside I use a vertical tank with a dipper and a lid just like the standard silvernitrate tank, this allows careful working with a low change of splashing/contaminating.

Working in the field I bring about 500 ml KCN fixer with me (in a plastic bottle, placed in another plastic container). When I fix I place the plate in a flat tray and gently pour about 250ml fixer on the plate, rock gently (fixing takes about 20-40 seconds), and than carefully drain back the fixer. I believe the amount of fixer in the drained plate is quite minimal. I wash, and discard the wash water in a tank, and bring it back home and flush it.

As said before: work with gloves and glasses and be focused! Stay away from acids.

Ok I'll finish with 2 remarks: A famous wet plate worker works bare handed, also puts his hands in the fixer OFF COURSE I WOULD NEVER RECOMMEND this, but he is very much alive and kicking, has been doing it for 15 or more years.

On disposal: you can use hydrogen peroxide, there should be a YouTube movie about this. Or you can put it in the hole of fire ant colony..as I read once..(this was a lighter note, do not know it was actually really done..;-)..)

Best,

Cor

Oh I forgot: KCN in my hands on WPC has a definitive edge: the resulting image is crispier, and the colour is more creamy than fixed with RapidFix

Kirk Keyes · Jun 10, 2010

Barry S said:
Yes. I should add the remediation of the used KCN solution with hydrogen peroxide before disposal and/or disposal as hazardous waste.

Unless you've been trained how to treat hazardous waste, I'd suggest not attempting it. Also, how do you verify that you've properly treated (eliminated all the cyanide, both free cyanide and cyanide complexed with silver) in your waste?

And it's not going to be a simple as just adding peroxide and all the cynide will dissappear. My understanding for the peroxide treatment, less reactive cyanides such as those complexed with silver may require addition of a chelating agent to encourage dissociation.

I happen to have a lot of experience with testing for cyanide in an analytical laboratory, and I know it takes a lot of specialized equipment, a few hard to find reagents, and some experience to get accurate results.

Barry S said:
I'm not sure the low residual concentration of KCN on gloves or in wash water warrants disposal as hazardous waste, but that's an option.

My understanding is that permissable effluent levels for cyanide are in the 0.2 to 10 mg/L range. You're local authorities will have better specifics than I do.

Kirk Keyes · Jun 10, 2010

mattmoy_2000 said:
If you do insist on using it, it's denatured by bleach, so have a large quantity of that to hand and soak everything that might be contaminated with KCN or KCN(aq) in it for at least 2 days. It produces some sort of gas and is very exothermic.

Cyanate ion is produced. Same as when cyanide is treated with peroxide. Bleach and peroxide are both strong oxidizers.

Kirk Keyes · Jun 10, 2010

Cor said:
Ok I'll finish with 2 remarks: A famous wet plate worker works bare handed, also puts his hands in the fixer OFF COURSE I WOULD NEVER RECOMMEND this, but he is very much alive and kicking, has been doing it for 15 or more years.

Anecdotal story:

A boss of mine started a jub at an major electronics test equipment firm many years ago. His new boss, was giving him the tour of the place and as they were walking past the gold plating tanks, the boss drops his new ballpoint pen into the tank. The pen starts to sink into the tank. Keep in mind, gold plating tanks are going to be in the 10-20% cyanide concentration range. The boss pulls his jacket off, slides his sleeve up, and thrusts his hand and lower part of his arm into the tank and retrieves his fancy new pen. He then walks over to the sink, rinses the pen and his arm off in water, and then pull his sleeve back down and puts his jacket on. The tour begins again as if nothing happened. My boss was shocked and amazed...

Lesson:

A single big exposure to some concentrated cyanide on your skin may not kill you - especially if you do a good job of washing it off. It's the much smaller dermal exposure for a long period of time, or the smaller oral exposure that is going to be a much greater risk.

mattmoy_2000 · Jun 10, 2010

Actually, the body is very good at detoxifying small doses of cyanide (hence why smokers don't die of accumulation of HCN). Evidently dermal exposure isn't definitely going to kill you, but if you have a cut or something, it's dangerous. The real risk with skin contamination is that you might contaminate something else which you then eat, or accidentally inhale the dust. Admittedly a quarter to half a gram is a lot to accidentally ingest, but it does burn mucous membranes (e.g. the mouth, eyes, nose, lungs).
Single, large (relatively!) doses of cyanide are what's dangerous, but you can be as careful as you like, accidents still happen. My rule is "don't use KCN unless you absolutely have to". Maybe I'm paranoid about it, but at least I'm alive.

Cor · Jun 11, 2010

Kirk Keyes said:
Lesson:

A single big exposure to some concentrated cyanide on your skin may not kill you - especially if you do a good job of washing it off. It's the much smaller dermal exposure for a long period of time, or the smaller oral exposure that is going to be a much greater risk.

Right! (still an amazing story though)

To expand a bit on this guy who does not use gloves, he once cut himself (not uncommen when working with glass plates and sharp edges(although you should bur(?) these first anyway)), he did not notice, and KCN came in the wound; he got a terrible headache and nausea, passed soon (the symptons that is).

As Joe said: some people can smell the almond scent, some can not. There are also people who are so sensitive they get an immediate headache when they enter a room with an open KCN fixing fray. I believe that KCN is partly a gas in solution (Kirk will correctly for sure).

I do not know if you can build op "resistance" against KCN by indigestion of small doses of KCN, just like the old kings did to protect themselves from possible poisoning.

A chemistry friend which has more knowledge than me on chemistry and safety commented that he was more worried of the CadiumBromide I used in WPC (I quit that in favour of ZincBromide) that the KCN I was using. His comment was that cadmium is an alien compound to the body, and strongly suspected carcinogen, whereas KCN can be cleared by the body (within reason...)

Having said all this: I do respect and fear KCN, each individual should make his own discion, BUT GET YOURSELF INFORMED!

Best,

Cor

thisismyname09 · Jun 11, 2010

Ammonium thiocyanate is known to be a fixer that is several times faster than thiosulfate. Perhaps if you use concentrated solutions / fix for a long time you can get it to start dissolving the silver out of the image. And its a whole lot safer than cyanide.

Shangheye · Jun 11, 2010

Can someone provide an example of the difference in tonality resulting from KCN vs Sodium Thiosulfate? I am going to to be doing WPC soon and am interested just how significant this all is on the end product. With the kids in the house I am note sure the value added is anywhere near worthwhile, but then I am uneducated about the results. K

AshenLight · Jun 11, 2010

Shangheye said:
Can someone provide an example of the difference in tonality resulting from KCN vs Sodium Thiosulfate? I am going to to be doing WPC soon and am interested just how significant this all is on the end product. With the kids in the house I am note sure the value added is anywhere near worthwhile, but then I am uneducated about the results. K

Take a look at this article http://www.johncoffer.com/Techsupport_files/MythBusters20090217addendum.pdf that has comparison plates made with both KCN and Ilford RapidFixer. I use KCN myself but only with extreme caution.

Ash

Cor · Jun 11, 2010

Shangheye said:
Can someone provide an example of the difference in tonality resulting from KCN vs Sodium Thiosulfate? I am going to to be doing WPC soon and am interested just how significant this all is on the end product. With the kids in the house I am note sure the value added is anywhere near worthwhile, but then I am uneducated about the results. K

Kal,

I would advice you to join the WPC forum at www.collodion.com. I did post a comparison there, but IMHO it is best to judge for yourself. And as you begin I would strongly advice to start with RapidFix, normal film strength until you get a grip of the process, there are so many variables involved in WPC and fixer choice is just one of them

good luck,

Cor

mattmoy_2000 · Jun 11, 2010

Yeah, I don't know about CdBr, but I was told that "CdCl is so carcinogenic it'll give your as yet un-conceived children cancer". I assume the chemistry is similar, as it's the Cd that's the dangerous bit.
That's one reason why we swapped to CdSO4 in the lab as a source of Cd ions.

Photo Engineer · Jun 11, 2010

Cadmium is a poison all by itself. The other ion does not contribute much to changing its properties. Therefore, if Cd were a carcinogen, I would expect all salts to share that property. Their effects may vary somewhat, but they would probably all share a degree of carcenogenicity.

PE

Kirk Keyes · Jun 11, 2010

Cor said:
To expand a bit on this guy who does not use gloves, he once cut himself (not uncommen when working with glass plates and sharp edges(although you should bur(?) these first anyway)), he did not notice, and KCN came in the wound; he got a terrible headache and nausea, passed soon (the symptons that is).

An indicator that it was cyanide poisoning would have been if his lips and fingernails turned purple.

Cor said:
As Joe said: some people can smell the almond scent, some can not. There are also people who are so sensitive they get an immediate headache when they enter a room with an open KCN fixing fray. I believe that KCN is partly a gas in solution (Kirk will correctly for sure).

I don't think I get the almond scent. But then I don't sniff almonds that much...

Some of the cyanide is released as gas - the amount is dependent on the pH of the solution and less is released as the pH of the solution goes up.

Cor said:
I do not know if you can build op "resistance" against KCN by indigestion of small doses of KCN, just like the old kings did to protect themselves from possible poisoning.

I don't beleive there is a tolerance or resistance to cyanide that can be "built up".

Cor said:
Having said all this: I do respect and fear KCN, each individual should make his own discion, BUT GET YOURSELF INFORMED!

This is the best advice of all!

Photo Engineer · Jun 11, 2010

You cannot build up tolerance to Cyanide. It kills you if you try.

I cannot smell HCN's bitter almond odor, but I can smell Almond oil. I only get a raspy feeling in my throat if there is any around, but then I have only been exposed to it a few times at very low levels. KCN is quite alkaline and can burn skin creating its own wounds! So, be careful.

Intravenous Hypo is one treatment for Cyanide poisoning.

PE

Kirk Keyes · Jun 11, 2010

Photo Engineer said:
Intravenous Hypo is one treatment for Cyanide poisoning.

Don't try THAT at home, kids!

removed account4 · Jun 11, 2010

Photo Engineer said:
Intravenous Hypo is one treatment for Cyanide poisoning.

PE

how do you know when you are "fixed: ?

Photo Engineer · Jun 11, 2010

I don't recommend any use of Cyanide, nor do I recommend any self treatment of any medical problem especially those related to chemicals.

PE

Anon Ymous · Jun 11, 2010

Photo Engineer said:
You cannot build up tolerance to Cyanide. It kills you if you try...

IIRC, some kings (like Mithridates) tried to build up tolerance to Arsenic. IDK if it's possible or not.

Ian Grant · Jun 11, 2010

Having run a lab where we routinely took in Cyanide solutions for testing for precious metal content and also been responsible for the parent company's collection, treatment and disposal I always treat Cyanides with extreme caution. We had a rigorous documented COSSH procedure, UK Health & Safety, which had to allow for accidents, methods of treatment.

These days the safety requirement (UK) is to be registered with the nearest Accident & Emergency Hospital, have their number clearly visible in all areas where Cyanides where worked with. Initially we had to have phials of Amyl Nitrate, but that had been stopped because from experience the Authorities found most was stolen for recreational use. We had a sterile Sodium Thiosulphate solution on hand but that wasn't a requirement, but could be used orally if someone didn't use a safety pump with a pipette, not that any of us did .

But in practice we were cautious, we had to acidify small samples of cyanide solutions, always done in a well tested fume cupboard. Larger quantities were routinely treated to drop the silver or gold out of solution before treatment to destroy the cyanide and every area was cleaned/treated to remove any possible traces.

However

Photo Engineer said:
You cannot build up tolerance to Cyanide. It kills you if you try.
PE

Quite wrong, in fact you can build up a degree of tolerance. I've seen this in practice where jewellery workers using Cyanide stripping (used to clean up castings) and also plating solutions would eat & drink at their work station, handling sandwiches etc with unwashed hands, totally illegal in practice. The worst culprit I met for this was still alive 20+ years later.

The smell of plating/stripping in a workshop if unventilated will make you feel queasy and sick, but these guys were so used to it, and often close by (opposite side of a small room) would be a pickling pot of boiling acid. But they really do build up quite a tolerance.

I do still use/treat cyanide solutions occasionally but it's not a practice I'd suggest to anyone without proper training in treatment & handling. A good friend has seen some commit suicide using cyanide and said it was a horrific death.

Ian

Photo Engineer · Jun 11, 2010

Ian;

I am not sure that you are correct. All of the information I have says that the lethal dose stays constant, but that people can grow accustomed to the symptoms of constant low dosage exposure, tolerating the shortness of breath and the sore throat. I think that it is a precarious position to take suggesting that one can grow immune to cyanide to any degree by repeated exposure.

It will kill you if you reach the standard LD. This is based on the chemical fact that CN ion bonds to hemoglobin more tightly than oxygen and at a certain level it will kill. You cannot change this reaction just by repeated low doses. Perhaps my choice of words was poor (toleration), but the fact remains that there is a level that kills, period.

PE

Ian Grant · Jun 11, 2010

I don't disagree Ron, my threshold is NOT going to get raised, the lethal dosage may be in the same ball park but the low grade symptoms/effects are certainly something the body can adjust for but it's not something I would would contemplate. It's too dangerous to use Cyanides unless you have 120% control.

Personally I don't ever want to endure a situation where the fumes are nauseous, or give you a headache, but that;s what happened in some sectors ofthe jewellery trade, and you can smell the Cyanide, it's a smell that I recognise instantly.

We won't disagree that safety has to mean what might appear over precaution.

Ian

CRhymer · Jun 11, 2010

Ron,

The main toxic activity of cyanide is as a cytochrome oxidase inhibitor.

Cheers,
Clarence

Photo Engineer · Jun 11, 2010

Clarence;

You are quite right, but how does it get into the cell? Via Hemoglobin and dissolving in blood! It can attach itself to hemoglobin much the same as Carbon Monoxide, a very close relative chemically. CO displaces Oxygen and kills by suffocation, HCN displaces some oxygen and gets into the cells killing them. HCN also dissolves in blood very readily thus forming a high concentration very quickly which is transported to the cells. Transfer across the membrane kills the cell.

At low doses of HCN with high Oxygen supply, HCN is metabolized by the liver. This is a rapid reaction and is why low doses can be eliminated quickly.

PE

argentic · Jun 12, 2010

Isn't there possibly another chemical less dangerous than cyanide, to produce the same effect of a better image than hypo?

Potassium cyanide fixer

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