reversal bleach

[camera8mm]

anybody ever used the clayton chemical reversal bleach sold by bhphotovideo. is there another source for this, as bh needs 4 minium order?
I cant find any other bleach to use for b/w processing.

[richard p. t.]

For black and white reversal processing generally people don't buy bleach but rather make it up from simple components. The R9 bleach is as follows.
12 ml of 100% sulphuric acid per litre of water
9 grams of potasium dichromate per litre of water.
That is it.
If using a different percentage strength acid, just add that much more (ie 75% acid, use 17ml per litre).
NEVER ADD WATER TO THE ACID but add acid to the water and wear protective gear when mixing and handling the acid.
richard

[christoph]

while i'm sure richard is aware of this, it should be noted here that potassium dichromate is *really* unhealthy, so one should be very careful when mixing and handling the solution. dont breath the dust and avoid skin contact, it's easily the nastiest chemical that you'll find in your darkroom (unless you're into exotic things).

the R-10 bleach is less of a problem, but unfortunately it doesnt work as easy as R-9.. it exhausts much faster and can result in emulsion damage under some circumstances, so it's best to always use fresh bleach (dont store it and dont reuse it often). also, avoid thiocyanate as a silver solvent in the fist developer if using R-10 and use thiosulphate or DTOD instead.

++ christoph

[christoph]

while i'm sure richard is aware of this, it should be noted here that not only the acid, but also potassium dichromate is *really* unhealthy, so one should be very careful when mixing and handling the solution. dont breath the dust and avoid skin contact, it's easily the nastiest chemical that you'll find in your darkroom (unless you're into exotic things).

the R-10 bleach is less of a problem, but unfortunately it doesnt work as easy as R-9.. it exhausts much faster and can result in emulsion damage under some circumstances, so it's best to always use fresh bleach (dont store it and dont reuse it often). also, avoid thiocyanate as a silver solvent in the fist developer if using R-10 and use thiosulphate or DTOD instead.

++ christoph

[Angus]

I'd be more concerned about technique of diluting the sulphuric acid. If you add the acid too quickly to the water, you can cause it to spit back or even to boil. OK so hopefully you're wearing eye protection but still conc. sulphuric is nasty stuff if you spill it. Your container can also heat up so rapidly that it cracks, even if it is pyrex. I've seen this happen.

So here's what I do....and bear in mind I work in a laboratory situation so I know what I'm doing. BTW the stuff you can buy won't be 100% concentrated. Don't worry, the stronger stuff is for universities and industry only.

I'm typically making 2 litres of dilute acid every time so I take a 5 litre pyrex beaker and pour in the required amount of distilled water for the solution I am making. I place the beaker of water in the sink and fill the sink with cold tap water up to the level in the beaker.

Then I sloooowly start adding the acid, perhaps 50ml at a time...stirring constantly. Occasionally I feel the outside of the beaker to see how hot it is getting. When all the acid is dissolved I leave the beaker to cool before pouring the dilute acid into a suitable bottle.

As for potassium dichromate, it's moderately unpleasant stuff but its OK for 13 year old school kids to use. Wash your work area and your hands thoroughly after use...its dangerous in the "don't eat it" category. As with any chemicals you don't want to go breathing the dust but its not going to do serious damage unless you start eating/drinking/snorting it.

[christoph]

As for potassium dichromate, it's moderately unpleasant stuff but its OK for 13 year old school kids to use. Wash your work area and your hands thoroughly after use...its dangerous in the "don't eat it" category. As with any chemicals you don't want to go breathing the dust but its not going to do serious damage unless you start eating/drinking/snorting it.

good advice with the acid. myself i use usually about 30% concentrated sulphuric acid where the handling is pretty safe if you protect your eyes. for those who are feeling really worried, use something even lower in the 10% range, even if it's a bit more expensive.

are you sure about potassium dichromate?
because i'm no chemist, but from my research potassium dichromate can be pretty harmful, because it can cause cancer. one drop on your skin once every few months probably wont hurt, but i became more and more worried when i was handling the stuff reguarly on a bigger scale. also over here in germany, you need to be over 18 to get it and sign a paper that you know what you're doing.

but apart from health/enviroment issues, personally i much prefer the R-9 bleach to the R-10 variant, it works much better and i even have the feeling the grain structure is slightly nicer. so if you're positive that it's pretty hamless if handled with care that would be good news.
++ christoph

ps: sorry for the double post above, seem to have hit the quote button instead of the edit button. in fact, i cant seem to find the edit button anymore on older posts.

[Angus]

are you sure about potassium dichromate?
because i'm no chemist, but from my research potassium dichromate can be pretty harmful, because it can cause cancer.

So do parsnips...and barbecued food...they are categorised as carcinogens...as are may things we handle in every day life.

From CLEAPSS Hazcards (the "bible" if UK school science health & safety)

Potassium Dichromate: May cause cancer, category 2 carcingen. Harmful in contact with skin, toxic if swallowed. Very toxic by inhalation. May cause sensitisation by inhalation and skin contact. Very toxic to aquatic organisms.

(Explanation....Category 1 - substances known to cause cancer on the basis of human experience.
Category 2 - substances which it is assumed can cause cancer, on the basis of animal evidence.)

Recommendations are that its safe to use on a small scale with Year 9 (ages 13-14) and older with goggles, consider nitrile gloves...for example dissolving 3g of potassium dichromate in 25cm3 of 1 molar sulphuric acid....Large scale oxidation experiments safe with Year 12 (age 16-17) wearing goggles and chemical resistant gloves.

So, its considered toxic and possibly carcinogenic but safe enough for a supervised 13 year old school kid to have a few grammes.

If you take basic care and wash everything well after you've used it...and don't use the equipment for food...then potassium dichromate is OK. Its not actually known to cause cancer in humans. Its not one of the nastiest chemicals that I work with, the powder isn't so fine that its likely to get up your nose, which would be the biggest worry...something as apparently safe as zinc powder is so fine it can get in your eyes and nose really easily as it hangs in the air and sticks to your hands...and that usually means a trip to hospital. Yet zinc isn't categorised as a harmful/dangerous chemical..its an essential nutrient!

[christoph]

hi angus,
thanks for the details..
i suppose those labels usually over exaggerating things, things like sodium carbonate (washing soda) or sodium hydroxide (lye) would probably be considered very harmful too. with sodium hydroxide i tend to agree though ;)
btw, whenever i dissolve sodium hydroxide (using your acid dilution cooling technique btw) i feel like coughing because there's a weird thing in the air.. do you know if this is normal? i usually try to breath as little as possible and leave the room as soon as dissolving is finished (and sometimes in between to get fresh air). takes the fun out of mixing D-94a though, so i might just switch back to D-19 with sodium thiocyanate as fist developer and R-9 for bleaching -- easier to work with, and i like the results a lot.

++ c.

[Angus]

Assuming you are dissolving solid sodium hydroxide pellets, yes there sometimes is an odour in the air which seems to almost stick to the lungs. Use plenty of ventilation, have open windows and work near one.

The reason why I would say sodium hydroxide and certainly conc. sulphuric are more dangerous to us than potassium dichromate is because you can have one or two accidents with the dichromate without harming yourself. Its not going to cause a container to break and spill nor is it going to spit out of its container.

One accident with the sulphuric, even just adding it to water too fast, and you can be disfigured for life or dead. With sodium hydroxide pellets you can seriously burn yourself if you handle them, and probably would die if you ate a few. Even the stuff you buy over the counter for cleaning drains is about 95% NaOh.

[CineGuerrilha]

if you need a supplier for the K dichrom you can get it from:

www.artcraftchemicals.com

[aj]

Well, it is not on their list

[camera8mm]

and where do I get sulfuric acid withoud emptying out my car's battery?

[Angus]

Sulphuric acid is a regular everyday laboratory chemical and as far as I know isn't involved in bomb making. In Europe at least I know some pharmacies sell it. Any company selling laboratory chemicals ought to sell it but not every such company sells to the general public, these are paranoid times we live in.

Remember you don't need concentrated sulphuric acid, you may be able to buy something already diluted somewhat. Battery acid is fairly strong in laboratory terms, typically 8-10M if memory serves, wheras the stuff you play with as a school student is usually 1-2M concentration.

[The_kodak_kid]

I'd be more concerned about technique of diluting the sulphuric acid. If you add the acid too quickly to the water, you can cause it to spit back or even to boil. OK so hopefully you're wearing eye protection but still conc. sulphuric is nasty stuff if you spill it. Your container can also heat up so rapidly that it cracks, even if it is pyrex. I've seen this happen.

So here's what I do....and bear in mind I work in a laboratory situation so I know what I'm doing. BTW the stuff you can buy won't be 100% concentrated. Don't worry, the stronger stuff is for universities and industry only.

I'm typically making 2 litres of dilute acid every time so I take a 5 litre pyrex beaker and pour in the required amount of distilled water for the solution I am making. I place the beaker of water in the sink and fill the sink with cold tap water up to the level in the beaker.

Then I sloooowly start adding the acid, perhaps 50ml at a time...stirring constantly. Occasionally I feel the outside of the beaker to see how hot it is getting. When all the acid is dissolved I leave the beaker to cool before pouring the dilute acid into a suitable bottle.

As for potassium dichromate, it's moderately unpleasant stuff but its OK for 13 year old school kids to use. Wash your work area and your hands thoroughly after use...its dangerous in the "don't eat it" category. As with any chemicals you don't want to go breathing the dust but its not going to do serious damage unless you start eating/drinking/snorting it.

Does the reversal bleach have to be a specific temperature? I’m using the same sulphuric/dichromate recipe here

[Angus]

I've used it at room temperature, which would be anything from 17 to 25C in my kitchen. I don't think temperature is very critical as you're looking to remove salts which have reacted with the first developer. It's probably wise to err on the side of caution and bleach for longer than you think might be necessary if the temperature is unusually cold.