Ward Burner Systems

customized combustion equipment

Infrared Energy & Raku Kiln Size

 

 

by Marc Ward
Clay Times Jan. 2005

 

    My wife, Kathy, and I just got back from a great weekend at Dan Finch’s in North Carolina near Raleigh. Dan has a wonderful nursery and pottery complex where he hosts pottery workshops. It’s a place for people to make pots, talk about pots, and fire pots. If you’ve never been to a workshop there, I highly recommend it. Anyway, this particular workshop was a Raku workshop with Steven Branfman, Charlie & Linda Riggs, and Marcia Selsor.


    All the workshop leaders made and fired clay. All the participants were inspired. All had a great time. The bonfire on Saturday night, designed by Kelly Finch was a pyromaniac’s dream. A forty-foot tall Eiffel Tower with music and fireworks. It literally exploded in flames… I’m sure it was noticed from the International Space Station. And just like junior high kids hopped-up on cola, hormones, and dance tunes, there needed to be a jerky assistant principal that was there to yell; “ Hey, you…yeah, I’m talking to you mister!,..NO running in the hall”. That’s where I came in.


    There’s nothing better than seeing the possibilities to get your creative juices flowing. But, many times, folks don’t understand the limits that need to be imposed on their aspirations. This came up several times in conversations at the workshop and I field similar calls on a regular basis. If a 3 cubic foot raku kiln works great, then a 6 cubic foot one will be twice as good. Oh, what the hell, if we make one that’s 15 cubic foot, we’ll get in lots of pots and make this one of the best raku kilns ever. Here’s where the “running in the hall” part comes in.


    Infrared energy is what we feel as heat. We turn our faces up to soak it in on that great sunny spring day. We hold our hands out to capture its warmth around a fall campfire. We also jump around like voodoo trance subjects trying to get away from our pants when we’ve stood too close and too long next to the raku kiln trying to extricate our pots. Infrared energy absorption is a function of the size and intensity of the energy source AND your distance from the source. You can be quite close to a small source, like a small peephole and deal with it or a good ways away from a large source of IR (infrared) and not be overwhelmed. But, as you get closer and the source or area of radiation increases, the heat you feel increases exponentially. This is the mistake that many folks make when designing a raku kiln.


    The size of the kiln and how you plan to approach it play a major role in the safety precautions you need to take. A small raku kiln that is a top-hat kiln and designed to be used with tongs, might be approached and dealt with in street clothes. The same size kiln that is a top-loader that you lean over and pull up and out from, might require the use of a face shield and protective sleeves. Same size kiln, but the top-hat (lift off) model “hides” the infrared energy from you. Now, instead of using tongs in these two situations, you have some high-tech gloves that you are going to use to pull the pots directly from the kiln by hand. Same temperature, but you’re 3 feet closer without the tongs. The intensity is magnified. With the top-hat kiln, you now need the same gear you used with the top-loader. With the top-loader and hand pulling you now need far more protection. You might need an aluminized hood and coat. Nothing changed as far as temperature, just your proximity and therefore your radiation exposure. This relationship becomes more and more critical the larger the kiln becomes. Bigger is not always better. Many times, folks call me and give me the dimensions of the raku kilns they are ready to build. I’ll plug the numbers into my putty-colored electronic brain and mention that this is a big raku kiln… a really big raku kiln. If you get over 10 cubic feet of raku kiln, it’s big. It’s not uncommon for people to design raku kilns that are 15-20 cubic feet. They are always surprised when I inform them that their teenage students will not only ruin their nails, but that their hair will most likely burst into flames…that usually gets their attention.


    Be cognizant of the power of infrared energy. Raku should be a fun process. If you don’t have the proper equipment or you’ve a made a kiln too large for your needs, the process will not be enjoyable. Before building, go to a workshop, watch and help others fire, get close to a raku kiln and get a sense of the heat generated by different sizes and openings. You can make and fire big raku kilns, just remember, you’ll need big protection from Mr. IR.