working with Potassium Dichromate

[Dakotah Jackson]

In looking at carbon printing the sensitizer is a Potassium Dichromate bath. I have read a number of things about how nasty this stuff is to work with. For those who do carbons and have used this successfully, just how bad is it? Do you need extra ventilation to work with it? A breathing mask? Or are the normal darkroom precautions of nitrile gloves, long sleeves and standing back a bit enough?

[BrianShaw]

For the "how bad is it" question I suggest you google a MSDS... which should be easily found on the internet.

I take the following precautions when working with dichromates: store the chemical in the original container; store chemistry out of the house in a padded plastic bin (Sterilite-type) in a location where my kids won't find it; measure using "chemical only" tools; mix dichromate solutions in a location that is out of the house (I use the garage since it is open and airy, yet dry and well-lit); store dichromate solutions in manner similar to the raw chemical; wear long sleeve shirt, gloves and dust repirator when handling; and work carefully to avoid spillage or splashing of dichromates.

I know there is a syndrome called "dichromate itch" but I imagine that there are worse affects that can be had from poor handling of these chemicals.

[BrianShaw]

http://www.jtbaker.com/msds/englishhtml/p5719.htm

[sanking]

I use both ammonium and potassium dichromate. The danger comes from inhalation of the dry chemical and ingestion. However, when dry dichromate is fairly heavy and very little of it gets into the air when mixing so very little risk is involved if reasonable precautions are taken. The solutions used in carbon printing are quite dilute, and used in very small quanitity. For example, to sensitize a sheet of 14XX20" carbon tissue I typically use only about 20ml of an 8% solution of dichromate, applying the solution with a brush.

Once the dichromate is in solution avoid drinking the solution (not something one would likely do) and wear gloves to avoid absorption by the skin. Gloves are very important because the combination of dichromate and warm/hot water used in carbon printing will result in skin irritation.

Sandy

[IanG]

There is a danger of ulceration, and wounds not healing up if you get dichromates near a cut or deep scratch. I know this from first hand experience, over 30 years ago I had a small cut or deep scratch on a finger (the type you get when fixing your car) and didn't notice it or the dichromate splash. So definitely wear gloves.

Ian

[BrianShaw]

ammonium and potassium dichromate

I believe the "dichromate" is the problem more than the potassium or ammonium (meaning that both will likely share the same hazards and precautionary measures) ... but here's the other MSDS:

http://www.jtbaker.com/msds/englishhtml/A5760.htm

[Bruce Pollock]

I have been making gum dichromate prints for a few years now and agree with all the previous cautions suggested, especially the rubber gloves and mask. I use a good quality paper mask (not the full respirator) but I'm usually only mixing very small amounts of dichromate solution.

Equally important, though, is disposal of the solutions. When I'm making gum prints, here's my procedure for dealing with waste dichromate solutions. Bear in mind that my methods use a very small amount (about 2.5 ml) of saturated dichromate solution. If you are using more, you might want to increase the amounts suggested below.

When making prints, I try to capture all rinse water and the developing water in a bucket. Generally after a printing session, I end up with about 4 litres of waste water in an ice cream bucket which will contain, at most, the 2.5 ml of saturated dichromate solution. Once I have finished the processing, I follow a procedure I learned from an article I found on the Photographer's Formulary site (I think it's since been moved). First, I mix about 2 tablespoons of sodium sulfite into the waste water. According to my research, this converts into a safer trivalent chromium compound (I sound like I know what I'm talking about). Then, I put in a couple of tablespoons of Drano (sodium hydroxide) and mix well. Then, I run the waste water through a Melita coffee filter (!!) and recover what I think might be shards of metallic chromium in the bottom of the bucket. I pour the waste water down my city sewer drain and have a growing pile of coffee filters, paper towel and other assorted bits which I haven't quite figured out what to do with yet but will probably just put in the regular city garbage.

I discussed this approach with local chemistry professor and he felt it was a safe way to dispose of the waste.

[eric black]

The MSDS and web-searches should give you a good idea of what to do with respect to types of gloves to wear. Something else that is just as important as how to handle it is how to store it. It is a strong oxidizing agent and will thus react with certain organic compounds (think solvents and other hydrocarbon-based developing chemicals). Although it wont react with everything, what it will react with can be quite violent in the right proportions. The take away message is that unless you know for sure its safe to store dichromates next to something organic- dont. Use as much caution on storage as you would with protective gear etc... Knowlege is king when dealing with chemicals like this- read and understand the MSDS and you'll be fine. Consult a local chemistry department you you have any specific compatibility questions- they should be able to help you out. Its been a few too many years since I got my doctorate in chemistry or Id offer up myself as a reference as well.

One more thing, wear clothing you dont care about when handling this material- if any spatters on a colored area of clothing, the color will bleach white almost instantly.

[Dakotah Jackson]

Thanks for the information. The outside storage and mixing where I live isn't viable at least half of the year. Mixing chemistry at 0 to 30 below in wind just won't work. Will have to do it inside with a good ventilation system taking the air out and blowing it outside.

As for disposal, any problems with putting it in a glass wide mouth jar with mesh over it so the liquid evaporates and any residue coats the glass? I do this with old selenium toner and every few years give the glass jar to the hazardous waste collection guys. Probably overkill but at least I don't dump it into the septic system or on the yard.

Mainly want to work safely and not cause problems. The MSDS sheets are interesting but so is the one for common water. Reading that might put one off drinking for a while.

[Kirk Keyes]

Don't worry about doing stuff outside. Dichromate usually often in crystal form and not likely to get into the air. Wear gloves, clean up spills, and there's low risk like most other photo chemicals.

[BrianShaw]

The MSDS sheets are interesting but so is the one for common water. Reading that might put one off drinking for a while.

As an aside that I will probably be the only one amused... the Los Angeles Department of Water and Power sends all residents an annual water quality report. Once one reads past all of the "college-boy chemistry analysis" one gets the distinct impression that they consider the LA tap water to be much better than any bottled water on earth.

[IanG]

As an aside that I will probably be the only one amused... the Los Angeles Department of Water and Power sends all residents an annual water quality report. Once one reads past all of the "college-boy chemistry analysis" one gets the distinct impression that they consider the LA tap water to be much better than any bottled water on earth.

Scientific surveys in the UK and elsewhere have shown that domestic tap water is nearly always far better than bottled waters, so they might be right :D

Ian