# toxicity of raku pottery



## quasi-starfish (Nov 17, 2008)

So I have a couple of raku pottery pieces that I think might look kind of neat in the new 90 gallon. They are heads, so it would be kind of Easter Island meets Angkor Wat, maybe.

Anybody have any ideas about the toxicity of raku pottery in an aquarium? The glazes have all sorts of heavy metals, but they are fired, but they are fired at a relatively low temperature. And of course, since it will be a planted tank, the water will be acidic due to the CO2. And I would plan to have red cherries in the tank, since they are in all my tanks.


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## Pooky125 (Jul 30, 2002)

My memories of raku glazes are a little hazy, but from what I remember, a lot of them are lead based. No raku pottery is food safe, as they'll leech toxic chemicals into your food and don't hold water, so I don't think I'd be putting them into an aquarium, especially with shrimp.

That said, if you sealed them with something, they might be ok.


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## Sharkfood (May 2, 2010)

You could spray them with a heavy epoxy or fiberglass resin, but it might make them shiny, which you might not like. Also, you may ruin your spray gun unless you have one made for blowing fiberglass or resin. Maybe that stuff is shiny to start with, I really have no idea. I'm ignorant in the ways of pottery.


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## mordalphus (Jun 23, 2010)

You can't use raku for eating or drinking because it's toxic... I'd assume that if it's toxic for you and me, it would also be toxic to your shrimp.


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## quasi-starfish (Nov 17, 2008)

Well, part of the reason it is not recommended for eating and drinking is because raku is rather porous - it has to be because of the rapid changes in temperature that it undergoes during the firing process. Porous pottery will harbor bacteria, so eventually you could get sick from bacterial contamination.

So, baring the question of toxic glazes, raku pottery in an aquarium may provide great sites for bacteria colonies.

Lead is not generally used in glaze in the US. We hear about lead because people bring back brilliant red pottery from e.g., Mexico, and the lead is responsible for the brilliant red color. The heavy metals I see in raku glaze recipes I found from a casual web search have e.g., cobalt, tin, silver, copper. Copper of course would be a problem for inverts.

The pieces in question were made as part of a university ceramics class. I expect lead-based glazes were not available - too dangerous for students to use. In addition, there isn't any red on these pieces.

A potential sealant I found on the web - mix 100% silicone with mineral spirits until runny, paint on and let dry. I suppose the mineral spirits evaporate, leaving just a silicone coating?


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## Betta Maniac (Dec 3, 2010)

Raku is a) toxic and b) won't stand up to being put in water (this is why you can't put fresh, cut flowers in a raku vase; not fired at a high enough temp).


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## quasi-starfish (Nov 17, 2008)

Betta Maniac said:


> Raku is a) toxic and b) won't stand up to being put in water (this is why you can't put fresh, cut flowers in a raku vase; not fired at a high enough temp).


I thought you couldn't make raku vases because the pottery is porous and they simply would not hold water.

On what time scale should raku break down? I've had the pieces in question in a bucket of water for the last several days (figured I'd leach out what I could) and I see no evidence that they are dissolving. Raku is fired to bisque before the raku glaze is put on and then refired. Does pottery fired to bisque dissolve in water?


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## mordalphus (Jun 23, 2010)

The raku glaze we used in my college classes was chock full of lead as well, there is no concern for students because we were told not to put it in our mouths.

You could completely coat it in silicone like you said, that would work.

A lot of underglazes are toxic because of their metal content, however they're made benign by the silica based clear coat (which is just like covering it with silicone). I had the great opportunity to take 3 years of ceramics courses and then TA for 2 years while I was in college. I was just talking to my better half the other day about maybe building a kiln so I could start back up. :\


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## quasi-starfish (Nov 17, 2008)

mordalphus said:


> The raku glaze we used in my college classes was chock full of lead as well, there is no concern for students because we were told not to put it in our mouths.
> 
> You could completely coat it in silicone like you said, that would work.
> 
> A lot of underglazes are toxic because of their metal content, however they're made benign by the silica based clear coat (which is just like covering it with silicone). I had the great opportunity to take 3 years of ceramics courses and then TA for 2 years while I was in college. I was just talking to my better half the other day about maybe building a kiln so I could start back up. :\


Cool, an expert. Can you look at the following pictures of the raku pieces in question? Can you guess the content of the glazes? 

To me it doesn't look like there is a lot of glaze on these pieces; rather, the dark color due to oxidation seems to be dominant, especially in the interiors. What do you think?


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## quasi-starfish (Nov 17, 2008)

Here's another idea for a sealant:

http://www.ptscoshop.com/starbond_em02_cyanoacrylate_adhesive.htm

The low viscosity would allow it to get into every crevice. Application might be a challenge though.

Hm, I wonder if something like this would be useful for sealing rocks to be used in an aquarium - i.e., to prevent leaching of calcium carbonate, for example. Could open up potential rock choices.


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## snowpea (Jul 21, 2018)

I know this thread is ancient but I'm adding to it anyways because I came across it searching for other information, but do have experience with (destroying) raku-fired pottery. I'm thinking the only way to safely treat any raku piece so that it will not leech any toxins or break down in the moisture is by resin infusion. You would need to find someone with a vacuum stabilization chamber. With the pieces submerged in the liquid resin the vacuum would suck the air out of the pieces and force the resin into the porous material. Afterwards, the pieces need to be baked to complete the curing of the resin. The heat can ultimately alter the look of the glaze, plus the resin will give it a shiny finish. It might be safer and more affordable to make molds of the sculptures with silicone and pour a resin copy, if they are small, but they appear to be quite large. As cool as it would look, I don't think it would be worth it; even if the glazes aren't toxic, the pottery is infused with smoke from the reduction chamber and may contain all sorts of volatile organic compounds, plus the pieces might even crack apart in the water.


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