Are there other ways to harden earth clays?

I do not have access to a kiln nor do i have the money to buy one. Are there other ways to harden the clay that will make it as hard or nearly as hard as a kiln would? I thought air drying would make it resonably hard, but nope it shatters WAY TOO easily.

EDIT: I should have noted that I live in the heart of LA in an apartment so I can't really make a kiln, but it seeming like i need to kiln it or buy some oven clay(I forogt the name) 

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aeray6 years ago
So... I work , part time, at a foundation that produces clay for ceramic artists. I actually make the clay that I and others, nationwide, use. While wood and gas fired kilns are fairly easy and cheap to construct, on a small scale, they are not appropriate for dense urban environments. A small electric kiln can be purchased for about $500, new.
However... when clay (correctly, a "clay body") is fired in a kiln, it is not just being dried, it is being vitrified to some extent. The mineral components of the clay body (in some clay bodies, this can be up to twenty distinct components) are being melted and fused together. As frollard points out, there are chemical reactions happening, but only those caused by intense heat; clay will never do anything but dry out at room temperature, and no significant chemical reactions take place. Concrete (or Portland cement), on the other hand, when mixed with water (the catalyst) undergoes chemical reactions (that produce heat, incidentally) transforming the original materials into something else entirely, which cannot be turned back into the original component materials.
If you simply dry out a clay body, by evaporation or low heat, then pulverize and reconstitute the body, you will have clay again,
If you fire a clay body to sufficiently high heat (enough to vitrify and harden it) and then pulverize it, you will have "grog", essentially sand, and no matter how much water you add, it will still be sand, just wet sand.

P.S. "Porcelain" refers to any number of specific formulations of clay, characterized by their high "whiteness",  handling (and mineral) characteristics, and a degree of translucency when fired to high temperatures (due to vitrification). Any old mud will not make porcelain, and, in fact, probably won't even make a workable, fire-able, clay.

aeray aeray6 years ago
Sorry, I got carried away. Simply put, no kiln = no hard. Electric kilns work well, though, as far as simple vitrification goes. There are also special fixtures (firebrick boxes with some kind of coating) that can be used to fire items in a common household microwave, but they are on the scale of a few cubic inches, while most kilns are measured in cubic feet. A small test kiln is around .5-2 cu.ft. and a "regular" kiln is around 5-7 cu.ft.. The big kiln where I work (which was originally used to fire bricks) is something like 4,000 cubic feet.
aeray aeray6 years ago
Oh, yeah... PPS... both of the links provided by others are pretty much useless crap. It's not just something you can throw together and get good results; the info and the science is out there (based on literally thousands of years of experience and knowlegde) and is easily achievable, with a bit of research. PM me, or call the Bray (from the link above) and I, or others, will point you in the right direction.

Sorry rickh and burf, but I've got to call it when and how I see it.
I haven't any direct experience of making a kiln but have made various forges in my time and they can get hot enough to melt metal.

However a recent Time team episode here showed a medieval expert making an earth kiln and baking pottery!

I guess it can be done as in the past they would have had fairly crude Kilns but still made successful pottery.

I can't verify the value of the link I gave just indicating it can be done. I bow to other expertise but with caution as i know this was done in the pas, with rather simple techniques.
The techniques themselves are simple, but the proper application of them can be difficult, and frustrating. Even experienced ceramicists have a pretty high failure rate, sometimes as much as 70%.
:-) Failure is all part of the rich world of Making :-)
Vyger aeray6 years ago
See, we got all kinds of experts here. Its what makes instructables so unique.
JimFritzMI1 year ago

Look into LTGS bricks. You can get bricks that are stable enough to build load bearing walls with no more than 140 degrees Farenheit.

EricA881 year ago

Just throw it in a camp fire- that's how it was done for thousands of years before there were kilns.

I know this thread is 4 years old, but the answer you are looking for is something called geopolymer, which is an alkali activated alumino silicate matrix binding aggregate together, which is basically what pottery is (clay is an aluminosilicate and grog, sand, are aggregates). What you want to research is Low Temperature Geopolymer Setting (LTGS) of which there is a manual available here:

and another link to actual pottery:

pojken6 years ago
What about this?

I want to try it and all that is needed, it seems, is a grill. It may not produce the best pottery, but to me that doesn't matter so much. I really want to find out more about it. I am thinking to email the author. If you come across any information, please let me know.

Burf6 years ago
Years ago, for a Scout project, my son's troop built a native American style pottery kiln which worked a whole lot better than I expected. Here is a link to instructions to build one for yourself:
frollard Burf6 years ago
+1 they're really easy to make a rudimentary kiln out of easy to source parts.

Air-drying is just the removal of the water, where firing it in a kiln changes it from mud to porcelain - a chemical reaction. Similar to how cement becomes concrete when it sets, just concrete does it without the immense heat.
aeray frollard6 years ago
Cement does not "become concrete when it sets" (except in a literal sense). Cement is a component of concrete, along with sand, aggregate, water, additives, etc. Also, when concrete "cures", not dries, the water is not removed, it is converted, through chemical reaction, into other components.
frollard aeray6 years ago
It's a nomenclature thing - agreed.

The cement truck shows up delivering cement, which is cast into my sidewalk...which becomes concrete when it cures.
rickharris6 years ago