Questions About Manganese In Clay, Slips, Etc

[JoshEdgarStudios]

Hello, I've been trying to figure out what route to go in regards to having dark brown to black clay to work with. I'm aware of the manganese toxicity, but I'm not that well versed in what to use that contains it.

 

I initially wanted to use Standard 266, but it was suggested to me to just use mason stains to get the dark color. I would prefer the method with the least effort-to-toxicity. Any help would be greatly appreciated.

[curt]

Stain

[GiselleNo5]

The dark brown, almost black clay that we use from Laguna does super bizarre things with glaze, bloats, cracks, and generally misbehaves. I would personally say that if you're going to use a clay like that, buy several kinds from several suppliers and test like mad to see if there's one you like. 

 

There's a potter who uses almost-black clay and it behaves well with her work and glazes. I'll see if I can find her site to share with you. Maybe she would tell you what clay she's using. 

[Tim T]

Depending on what you want to do, some earthenware clays can be fired to a very dark brown without bloating - the piece below is just earthenware with some white slip in the indents, and a matt clear glaze over the top to stick it together and make it waterproof. Even if it isn't black enough for you, it'll reduce the cost and your toxicity worries, and probably behave better than black clays, which I have also heard are a pain to work with.

Have you thought about just using a black slip instead?

[GEP]

Most black mason stains contain manganese too.

 

As long as you are aware of the risks, managing the danger is not that tricky. Don't eat or inhale it. When firing use a proper kiln vent. Stuff that you should be doing in general anyways, due to ALL of the potential hazards in your studio.

[bciskepottery]

Go to the main forum page and do a search on manganese . . . there are a number of threads that have discussed the use of manganese, safety concerns, proper handling, etc. 

[JoshEdgarStudios]

My main concern is the long term effects of using stuff with manganese. Also, once fired, is there any hazards to holding/using the piece?

 

Anybody know any good stains that can achieve the dark brown color of Standard 266? I don't have the ability of mixing my own materials at the moment, so I'd prefer something ready to use.

[bciskepottery]

Here is a link to Standard's 266 Safety Data Sheet: http://standardceramic.com/wp-content/uploads/2015/09/MSDS-112-710.pdfNote -- the percentage of manganese in 266 is around 1%.

 

If you are in clay for the long haul (or even the short haul), learn your materials and understand the risks associated with them and of what they are made. Then, don't do stupid things. The risk from manganese is greatest from inhaling dust (not unlike general clay dust and silicosis). If you practice good studio hygiene, you can minimize your risk. If you sand your bisque 266 bowls -- better wear a respirator. Like many toxins, the danger is from a build up over time. Your body naturally has some manganese in it; some vitamins include it . . . the key is keeping the level to within acceptable limits.

 

As Mea mentioned, manganese is often used in colorants -- especially black; so adding a stain that uses manganese does not necessarily eliminate the problem. The manufacturers of stains and colorants are all required by law to post safety data sheets that show what is in the material (and, I believe, to give you a copy if you buy the item). So, learn what is in what you use.

 

The primary colorant in 266 is red iron oxide (around 10%), plus a touch of manganese (around 1%). You might be able to work up a wash of red iron oxide and cobalt to give you a similar color (cobalt is also used in some blacks). You will have to experiment to get the ratio that gives you the color/hue that you are looking for. But, mixing materials from powdered forms carry a risk . . . so learn of its risks and how to mitigate them.

 

You might be able to mix underglazes to give you the color you want. But, some underglazes encapsulate materials that could be risky or leach. When you mix them, you create new versions and the manufacturer's statements of non-toxic, food-safe, etc. no longer apply.

 

If you are not in a position to mix materials, your best option might be to learn to use 266 and minimize your risks through safe handling and studio practices. I've been using 266 for years, as have others. It can be done.

[JoshEdgarStudios]

bciskepottery, thank you for the information. I was looking through the other related treads, but didn't find what I was looking for. I believe I will just try out the standard 266 and see how it goes.

[NancyAmores]

Sheffield Pottery has a black earthenware that gets its color from clay content according to their site, I haven't used it but their red stoneware and porcelains are lovely. Pricey but shipping's included.

[GEP]

http://rarediseases.org/rare-diseases/heavy-metal-poisoning/

 

Just for some perspective, here is a webpage that gives an overview on heavy metal poisoning. In addition to manganese, this organization considers the following metals, commonly found in pottery studios, as poisonous too:

 

Aluminum

Chromium

Cobalt

Copper

Iron

Nickel

Tin

Zinc

 

Plus these metals, which not as common, but still used by some potters:

 

Barium

Cadmium

Lead

Lithium

 

 

Working in any pottery studio means you need to practice good safety habits. And if you practice good habits, you can safely work with manganese too. Not sure why manganese gets such a bad rap, compared to all of these other metals. I think a handful of (not proven) horror stories have created the fear. In the case of David Shaner, who died of Parkinson's disease (suspected to be caused by manganese poisoning), he was also known to stir his saturated glazes with his bare arm. That's not a good safety practice, he probably ignored many others. And who knows he could have been poisoned by a combination of metals. Or he could have developed Parkinson's in the idiopathic ways that non-potters get Parkinson's.

 

Manganese should be taken seriously, but not disproportionately to all of the other potential poisons in your studio.

[Guest JBaymore]

There is a large level of misinformation in the studio pottery community about various aspects of toxicology of the materials we handle.  The key to negating this influence is getting good solid information about the subject.  There ARE good references out there....you just have to make the effort to find them.

 

Two huge assumptions that are both wrong:

 

• Because it is art materials... it is all OK to handle.  It's art for crying out loud!
• Oh my god, that stuff contains xxxxxxxxxx ..... we're all gonna' DIE!

 

There is a lot of misinformation in the studio pottery community surrounding manganese.  A lot of the studio pottery community has heard information about horrible events attributed to manganese that are totally apocryphal.  Meaning.... no proof.  Assumptions made.  There are good scientific studies that show that manganese has the capability to cause some serious issues.  But you need to understand the WAY that manganese enters the body, and the magnitude of the exposure that is implicated, and the extent of exposure that has to happen.

 

One of the most basic tenets for understanding toxicological impacts:  Intensity, Duration, and Frequency

 

Manganese dioxide ( the common form potters use) is not absorbed thru intact skin.  Skin contact is not an issue.

 

Respirable DUST is the main problem with manganese for studio potters.  And the main potential source for that problem is sub-micron fume dust particles from manganese vaporizing out of glazes, slips, and clay in the kiln. 

 

Respirable dust is the main problem for studio potters for just about ALL of the materials we use.  You want to have something to worry about......... it is SILICA dust.  Look it up.  It is not only about silicosis... it is about lung CANCER too.  Controlling clay and glaze dust in the studio is you number one priority.  Because it is sourced just about EVERYWHERE. 

 

If you control that problem appropriately (you likely cannot totally eliminate it) ........ then the smaller amount of dust containing manganese particles coming from manganese bearing slips, clay bodies, and glazes will also be decently controlled.

 

If you are not controlling the dust sources in the studio... then adding a manganese bearing source of potential respirable dusts is just compounding the potential issues.  You'll use less volume of manganese bearing slip to color the surface of the clay than you will if the whole (dust producing) clay body contains manganese.  So that is the better choice if both options give the eresults you want.  You'll also FIRE less mass of manganese in the kiln... thereby producing less manganese fume.  So that is the better choice.

 

best,

 

..........................john

[JoshEdgarStudios]

Some really good information here. Thank you all who've replied. Very helpful and enlightening.