[Clayart] Cobalt Carbonate toxicity

Vince Pitelka vpitelka at dtccom.net
Wed Dec 16 21:18:55 EST 2015

Let's not overreact.  Cobalt carbonate and oxide are not water soluble and are not absorbed through the skin, so no need to wear rubber gloves unless you are really getting your hands right into the glaze a lot, and then it's certainly a good idea to wear the gloves.  When handling or mixing any dry clay or glaze materials one should always wear a respirator with P-100 cartridges, but no need for a respirator when using liquid glaze.  There is no evidence of any cobalt release when it is locked in a stable glaze.  
- Vince

Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka at dtccom.net   

-----Original Message-----
From: Clayart [mailto:clayart-bounces at lists.clayartworld.com] On Behalf Of Mary Winter via Clayart
Sent: Tuesday, December 15, 2015 7:14 PM
To: Clayart international pottery discussion forum <clayart at lists.clayartworld.com>
Cc: Mary Winter <mary8252 at gmail.com>
Subject: Re: [Clayart] Cobalt Carbonate toxicity

Hi Des,

Yes cobalt is a heavy metal and is poisonous in it's raw state and dangerous in powder state. When mixing and using a cobalt glaze wear a good respirator with cartridges rated for this and wear rubber gloves. Heavy metals once in the body don't leave, their levels build up over time.
Cobalt is absorbed through the skin as well so wear the rubber gloves. The fumes in firing are not to be trifled with either. Heavy metal poisoning from the cobalt most likely wouldn't happen from one exposure but over time. Once the cobalt has been fired and is trapped in a glaze matrix, depending on the concentration and the degree to which it is fired, it will not be toxic anymore.

Hope this helps


On Tue, Dec 15, 2015 at 3:03 PM, Teri Lee via Clayart < clayart at lists.clayartworld.com> wrote:

> Hello, Des,
> The toxicity is mentioned in John Britt's section on cobalt oxide, and 
> seems to extend to all cobalts:  "Cobalt is toxic (similar to nickel) 
> and should be handled with care." He issues the same caveat with coppers:
> "Copper materials are toxic and should be handled with care." As I 
> mentioned in my earlier post, I'd like to know if cobalt carbonate, 
> once glazed and fired to cone 10, is safe. And, just to expand my 
> knowledge base, I'd appreciate if anyone knows whether cobalt oxide 
> and/or copper carbonate is also safe in glaze form after a cone 10 firing.
> Britt's references appear on page 23 in the paperback edition of "The 
> Complete Guide to High-Fire Glazes."
> Teri Lee
> Date: Tue, 15 Dec 2015 09:14:18 +1100
> From: Des & Jan Howard <djhoward at hwy.com.au>
> To: Clayart international pottery discussion forum
>         <clayart at lists.clayartworld.com>
> Subject: Re: [Clayart] Cobalt carbonate toxicity
> Message-ID: <566F3F3A.4010609 at hwy.com.au>
> Content-Type: text/plain; charset=utf-8; format=flowed
> Teri
> If you don't mind could I have the page or section reference please?
> Des
> On 15/12/2015 5:24 AM, Teri Lee via Clayart wrote:
> > I've been reading about Cobalt Carbonate toxicity in John Britt's
> excellent
> > book on high fire glazes. As someone who never took chemistry in 
> > school, I'm a bit confused if cobalt carbonate is mainly dangerous in its "raw"
> > form, but after being mixed in a glaze and fired to cone 10, it is 
> > no longer toxic. I'm especially concerned about using cobalt 
> > carbonate in functional ware. Thank you.
> --
> Des & Jan Howard
> Lue Pottery
> Lue  NSW
> Australia
> 2850
> 02 6373 6419
> www.luepottery.hwy.com.au
> -32.656072 149.840624
> _______________________________________________
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