Aquascaping with fired clay--clay type toxicity

**woodenfish** · 10-11-2007, 05:17 PM

I am thinking about using fired clay for rock work for discus tanks.

I want to make cliffs and caves etc by hand with clay and then fire.

Are not all clay types safe? Do some contain metals?

Those of you who have used fired clay with no toxicity problem please state the clay type that you used.

A source for clay gives the following choices:

>Low Fire White Moist (Smooth no Grog Cone 06-04)

>Low Fire White Sculpture (Same as above with Some Grog)

>Low Fire Indian Red Moist (Smooth no Grog cone 06-2)

>Low Fire Terra Cotta (Same above w/ Some Grog)

>New Stoneware RUBY STONE (Firing range is Cone 4-7 , at Cone 6 it is a Beautiful Orange/Tan Color, Lightly Grogged and great for Dinnerware and Functional Pottery as the absorption is a low 1 1/2 % at cone 6)

>Buff Stoneware (Wide Range Creamy Beige Clay cone 04 - 7 with Some Grog)

>Brown Stoneware Clay (Cone 4-7 Medium Dark Brown Clay with Manganese Specks and Some Grog)

>Rustone Stoneware Clay (Cone 4-7 Dark Brown Clay no Specks , Some Grog)

>White Stoneware Clay (Cone 6-10 White Stoneware with some Grog)

>Speckle Tan Clay (Cone 4-7 Medium Tan Clay with Manganese Specks and Some Grog)

>Mid Range White Porcelain Clay (Cone 4-7 Smooth domestic Porcelain clay NO Grog)

>Barbs Body Stoneware Clay (Cone 5-10 Very Nice Stoneware that fires to a Tannish Gray Color)

>Mather Stoneware Clay (Cone 6-10 Production Body suited for making Ovenware & Functional Dinnerware)

>Mather Porcelain (Cone 8-10 Smooth High Fire Porcelain Clay that is easy to work with fires well in Oxidation or Reduction)

>Raku Clay (Cone 04-7 The Ultimate in Raku Clay Bodies that contains a blend of Fine & Medium Grog for Thermal Shock Resistance common in Raku Firings)

What would be some of the best choices, both safety and appearance?

Is Low Fire Terra Cotta the kind for many planters? Is low fire easier to find kiln for?

Do you think it is easy to find a kiln (to use) that is big enough for aquascaping?

**Harriett** · 10-13-2007, 10:41 PM

The low fire clays range from the 0s to about cone 2; medium fire clay which is commonly called stoneware will be cone 3-7; cone 8-10 is high fire white porcelain. My guess is this, if you are going to ask a potter to fire the clay for you: the higher the cone the higher the temperature needed to reach the cone level and the longer period of time the piece needs to be fired, thus more expense. Kiln space is always limited and another guess would be that if someone is willing to fire for you, the caves,etc need to be in smaller pieces that you later silicone together in the tank. If you are going to take this on, you need to do some research on clay preparation [for example if the clay is not thoroughly kneaded before you work it, then when you fire it the air bubbles trapped inside will sometimes blow up the piece and any other nearby pieces that it may hit in the kiln; if the thickness of your pieces is not consistent or if they are too thick, your pieces may crack, etc]. The fired clay will look quite different depending on whether it is reduction or oxidation fired. Skip the raku--wrong application. You need to find out what kind of kiln it will be fired in. I don't know if clays with metals like manganese will leech into the water. Grog is just clay particles and bits that were previously fired and then ground up and added to the fresh clay as a stabilizer. Low fire is adequate if you like the look. You'll have to call around to find someone willing to fire your pieces---the little shops where old ladies paint molded greenware pieces and then they fire them for you might be willing to work with you. Those are low fire operations with oxidation kilns.
Best of luck
Harriett

**woodenfish** · 10-14-2007, 03:24 PM

Thanks

My biggest concern is impurities such as metal. I need a clay that does not have any metal, besides low fire.

I have already asked around for pottery clubs in my area for kilns for use or firing service.

I know that the kilns will likely not be very large, so I have to make sure that the smallers pieces have relief features (flat surfaces) that allow fastening with nylon bolt and nuts or epoxy glue.

My major concern again is in choosing a clay that does not have impurities that can leach into the water.

Is the basic terra cotta a good choice? What accounts for the red color? I hope it is not iron, but I have rountinely used terra cotta clay planters in tanks for years without problem. If I can find the same material, I believe it should be OK.

Do you think that the terra cotta clay among the choices is the same material as in many terra cotta planters?

I will ask the seller for sure, but I would like some preliminary knowledge. Are they many terra cotta formulations etc?

**Harriett** · 10-15-2007, 02:45 PM

I have a few made made terra cotta low fire egg lay caves, etc that I've gotten at shows for dwarf cichlids. I have used them and never had a problem with fish health. Terra cotta is red because of the iron content--I may be mistaken but I don't think it leeches into the water after it's been properly fired. There are more formulations of clay bodies than you can shake a stick at [--how many recipes are there for sugar cookies?]. Your best bet is to talk with the clay source you are considering buying from and find out directly what the recipe is. A regular low fire terra cotta or a standard higher fire stoneware can be had without the metals--those are added for visual effects but the clay can certainly be mixed without. Tell them what your application is and work together.
Best of luck
Harriett