Whoops, sorry for taking so long to get back to you on your questions.
Basically raku clay is(oh sheesh, to the best of my recollection and I don't have my nelson handy) of a courser mix, meaning there is a higher grog content so the pieces don't blow up or crack during the shocking process of the rapid firing to temps and rapid cooling. Draw back is it generally isn't as plastic and(in my experiences) more difficult to throw on the wheel. The concept here is to keep your piece in tact while going through the thermal expansion and contractions. The point of quarts inversion(I believe around 900-1000F) is a critical juncture for any clay body, both on the way up and down in temps. Again, since the raku process is so shocking to the clay, there are specific clays designed to keep the shock to a minimum.
However; that being said, I have always for the most part just used regular high fire stone ware. Back in college, we'd just use the same stuff we pugged out of the mill. There will always be a percentage cracks or popping or flaking using this type of clay, but it has never been such a big issue as memory serves me. Of course, if you are going to order premixed clay specifically for raku firing, you might as well just get some raku clay. Remember though you will lose an amount of plasticity so I'd suggest ordering some stoneware clay too and experimenting with both. also if you are still thinking of doing a primative firing(such as just putting pieces directly into a camp fire or the equivelant) a raku based clay would prove bennificial as well. One thing you will want remain aware of is to take care not to get the two bodies mixed together(especially if they have different maturing temperatures) for future use.
If you(or your potter friend) have access to mixing your own clays, you can just add some 200 mesh grog with your regular clay body. The added safety feature is that if you do accidentially mix them up, the additional grog will not be any main factor of concern.
I also remember using a porceline body for raku as well(you know in college, why not experiment). The maturing temp is not that big a deal if it's not going to be functional ware. So a cone 3 clay body will do just as fine for the project as a cone 10.
On the subject of raku again, I noticed while paging through the Axner Supply site, they have prefabed raku kilns. They actually look pretty sweet compred to raku kilns we've built in the past. We're talking kilns with cranks and a chain much resembling a well with an upside down bucket. As i said, they look pretty slick, but I think the costs ranged from US$2500-4500. A little expensive for my taste when you consider the added features are merely ease of placing and removing the ware. Heck, I still say build your own kilon, especially if it is for raku. You can build your own from a 55 gallon drum with a small burner and insulating fabric for a few hundred bucks. And I believe you told me before you have welding capabilities at your shop, so I vote for making your own. And just think of the added satisfaction you'll get knowing you did IT ALL by yourself. that goes a long way in my book FWIW.
I'll post you more on the subject later on. such as glazes to use(but one of my nicest raku pieces is(coincidentially) a mask I titled "Aging" where I used a low fire englobe by accident. The result was that the glaze crazed in a big way seperting(not from the clay but from itself) by about 1/8 inch, hence it looked like a really old wrinkled face and that's where it got it's name, Aging. after i did the raku firing though on it, I coated it in a very low fore clear glaze to gloss over and bond the englobe to the clay permently- I did that a few weeks later because i noticed some of the glaze was flaking off the piece. I guess what I'm saying is there are infinite possibilities. And while there may be more optimal bodies or glazes to use, you can get striking results by accident and give your piece that unique look to it.
Not only am I babbling now(you cah tell I like to talk about clay<G>) I'm wanting to get back to work at the moment. I got me a good nap in this afternoon with the intention of pulling an all nighter here this evening so I want to get busy.
Let me know if you have more questions or what you decide to do.
And most importantly, have fun :)
P.S> Just since I started this message to you, our weather has tken a complete nose dive. Skies went from n evening clear blue from the east to an omnious BLACK from the west. Temp dropped dramatically and we are getting winds that look/feel about 30/40 mph. Cold front is definitely setting in. Time to hole up once again, grrrrrr.
PPS> In my thhread header, there is a link to Axner and a few other places where you can get prices on burners, fabric wire, tongs, and etc. Take a glance through some of them if you have time. If not, when I get around to it, I'llpull up some links to what I consider appropriate burners and other stuff ytou'll need to build your own. Remember also, I'm suggesting build it from an old 55 gallon barrel, so you can perhaps already begin to get a visual of what you're gonna be involved with.
Okay, I'm back to work. Talk to you later on. |
