Cobalt oxide safety

[rox54]

I am interested in using a cobalt oxide wash on leather hard clay but am concerned for my safety as well as food safety. I can't find information on this site, but found enough elsewhere to suggest that I should use it with caution. Any advice would be greatly appreciated.

[liambesaw]

Don't lick your fingers or inhale the powder and you'll be just fine.  You can wear latex gloves if you think you might get it on your hands.  

[rox54]

21 hours ago, liambesaw said:

Don't lick your fingers or inhale the powder and you'll be just fine.  You can wear latex gloves if you think you might get it on your hands.  

Ah, thank you! I think I can mind those rules!  I experimented with it on one coffee mug and would like to move forward, but was also concerned with food safety since its on the rim. I fired it to cone 6 with a clear glaze over top. 

[kristinanoel]

Would love to see a photo of what you did! I am always in awe of the ancient pottery with cobalt  designs, I've tried to use it as a wash and it gets EVERYWHERE.

Worse than iron. 

Ok, kidding. nothing's worse than iron. 

[Callie Beller Diesel]

Because it was raining and cold yesterday because that’s how the May Long Weekend works in Alberta, I did a bunch of hunting on specifics for cobalt metal (not salts) and their assorted toxicity levels. The rabbit hole involved a really embarrassing number of internet tabs, and a bunch of weirdness. I had a big long thing written, but it was too long.

The highly condensed version is that acute toxicity from cobalt carbonate would be very expensive and unlikely due to the amount you’d have to ingest (46g for a 150 lb woman) , and cobalt oxide is even more so (almost 450g for that same 150 lb woman). That said, both carbonate and oxide are classified as human carcinogens. Data involving cobalt toxicity over medium or long term exposures of lower levels mostly seemed to involve salt forms of cobalt, which are FAR more soluble (take note, those who work with fuming!). Side effects included cardiomyopathy, various neuropathies and interference with the thyroid that lead toAll of these instances involved daily exposures to 8mg daily with alcohol (it was in a beer foam stabilizer), or 15mg daily in the form of iron supplements back in the 60’s. They couldn’t measure the amount from the damaged hip replacement parts for obvious reasons. 

 Normally, I would refer to water quality guidelines for potential limits, but the only ones I could find in Canada pertained to soil amendments for ruminants,  or the potential for cobalt left over from nickel mining would affect water tables. As it turns out, cobalt metal forms are REALLY not soluble, and wind up as precipitate very quickly, so no Canadian municipalities test for it, because they don’t have to. The salt forms that do manage to dissolve get taken up by algae and aquatic plant life pretty quickly. It is bad for fish and invertebrates though. Any water quality recommendations are either tailored to these smaller life forms, or are a bit larger so that cows aren’t getting sick from not enough B12.

There does not seem to be numbers based data on the exposure that “artisanal” miners experience in the DOC, where much of the world’s cobalt reserves are. That whole situation is truly appalling. Suffice it to say though, I don’t think anyone in Western countries are exposed on that level. They shouldn’t be either. Cobalt comes from other places too. Please inquire about your sources.

 

 

 

Anyways. My conclusions are 

As with many things, the risks are far greater from the raw material, and are more applicable to the potter than the end user. Cobalt oxide and carbonate, being VERY powerful colourants, are unlikely to be leached out of pottery in a quantity that will be harmful acutely, or even harmful long term in the amount you apply for a wash on the outside of a mug. Also, you’d need to ingest it, not just have it rub off on your hands. So if it’s on the outside of a mug, you’re probably good. 

One other thing I did find was that cobalt does become more soluble (again this pertained to the salts) with exposure to a mild base. I’m thinking of dishwasher detergent here. If you wanted to be really paranoid about it, it might be a good idea to cover it with a clear glaze, for durability’s sake. 

 

[rox54]

4 hours ago, kristinanoel said:

Would love to see a photo of what you did! I am always in awe of the ancient pottery with cobalt  designs, I've tried to use it as a wash and it gets EVERYWHERE.

Worse than iron. 

Ok, kidding. nothing's worse than iron. 

Thanks for asking! I slip-trailed then did an oxide wash. Easy and fun to do.

ETA It is a loosely designed bamboo leaf btw! I stamped it before slip-trailing.

[rox54]

3 hours ago, Callie Beller Diesel said:

Anyways. My conclusions are 

Wow, I can't thank you enough for the time you put into this! I was getting frustrated in my search, probably because of how I went about it. I was looking at "ceramics/safety" and not having much success. You wouldn't think it would be so hard!

[Callie Beller Diesel]

I mean, there’s not a huge amount of ceramic safety issues regarding cobalt because we’re not exposed to enough of it, so those search terms won’t bring it up. When there’s no data available for potters and cobalt based illnesses and we’ve been using this stuff for hundreds of years, you’ve got to wonder a bit.  So then you have to think “who else handles this stuff, and how do they get sick (or not) doing it, and can those circumstances be replicated somehow in my studio?”

Some fuming processes that use cobalt salts could and do definitely present health and safety issues. Cobalt wash? Not impossible, but highly unlikely. 

Also, that mug is lovely!

[liambesaw]

2 hours ago, Callie Beller Diesel said:

I mean, there’s not a huge amount of ceramic safety issues regarding cobalt because we’re not exposed to enough of it, so those search terms won’t bring it up. When there’s no data available for potters and cobalt based illnesses and we’ve been using this stuff for hundreds of years, you’ve got to wonder a bit.  So then you have to think “who else handles this stuff, and how do they get sick (or not) doing it, and can those circumstances be replicated somehow in my studio?”

Some fuming processes that use cobalt salts could and do definitely present health and safety issues. Cobalt wash? Not impossible, but highly unlikely. 

Also, that mug is lovely!

Is fuming cobalt a thing? I didn't think kilns got hot enough for that

[Callie Beller Diesel]

@liambesaw Back in the day there was a couple of raku artists that would spray their pots with one of the cobalt salts for some truly beautiful results, but I expect there’s some solid health and safety reasons people don’t do it a lot anymore. I want to say they used cobalt sulfate, but I’d be lying if I said I remembered exactly.

[liambesaw]

31 minutes ago, Callie Beller Diesel said:

@liambesaw Back in the day there was a couple of raku artists that would spray their pots with one of the cobalt salts for some truly beautiful results, but I expect there’s some solid health and safety reasons people don’t do it a lot anymore. I want to say they used cobalt sulfate, but I’d be lying if I said I remembered exactly.

That is... Scary as hell.  If anyone reads this in the future, never SPRAY any metal salts, ever.  They're all toxic, and don't provide anything special that you can't get some other way.  The spray itself, toxic, the fumes from evaporating when it hits hot pottery? Toxic.  And toxic in some of the worst, most heart breaking ways.

Sheesh. But that's not fuming, fuming is introducing the salt (preferably as a powder) to the kiln during cooldown.  Still hazardous, especially if firing indoors, but not nearly as hazardous as spraying the salt mixed with water!

 

[Callie Beller Diesel]

@liambesaw agreed on all points.