Hi Crocodile.
Sorry for the delayed response, days are usually busy for me and I wanted to respond to this in a proper manner.
That being said, I'm happy to see someone else here on SI has an interest in ceramics. Of course, I'm not surprised you happened along here, not one bit :)
And I'd be particularly interested in hearing anything about kiln construction and fuel-firing systems.
Okay, we'll start this thread off discussing kilns. Or as some call it "living with the dragon"<G> If you've ever been around a large fuel kiln reaching temps upwards of 2300°F, you would fully understand the above term :)
Determining which kiln is right for you will depend on a number of factors. I will run through the different types first(with some added commentary I'm sure) than we can determine which might serve you best.
Electric Kilns:
These are nothing more than glorified ovens.
They use heating elements that resemble coiled springs. The most common type, and that which you described are called paragon kilns. They come in a variety of diameters and are sectional as you mentioned. There are also a good number of manufactures of these. Mine is a Skutt® 30" diameter and I have four rings(sections) that are each 10" high. I mostly use mine for bisque firing my pottery. It's still here in my garage(my gas kiln has since been moved to another location- more on that later). As I understand it now days universities have venelation systems for the electric kilns as well. I don't have any special venelation for mine- I might have the garage door opened a foot or so just because. But unless you are working next to it for extended periods, I do not think it is mandatory- mixing glazes is a completely different stroy.
On mine, each ring has it's own temperature control which are tied into a central timing unit. You can set the timer as a safety precaution so you don't over fire, but the kill switch is triggered when a steel arm that reaches in through a special hole and rests on a "pyrometric cone" drops as the cone melts. Different cones melt at different temps. It is improtant to use small cones whit electric kilns as opposed to larger cones that are used for gas kilns. The bisque firing is relatively simple and can be summed up as "hit or miss". All you want to do is take enough moisture out of the piece so it can be handled during the glazing application with out breaking. If you fire it too high, glaze will not stick to pieces.
Gas or propane kilns
These are the ones that are usually larger and are depicted in the image of most production potters, sculptures, and universities. There are also a large number of manufactures. But I know a lot of people who prefer to build their own. I have built several. My current one though was built by a company called West Coast Kilns- I simply did not have the time to build my own as I was working at a very full time job when I moved back here. It was more cost effective to do it that way, and they build kilns that will last for many many firings. Perhaps the last kiln an individual will ever need, assuming he/she doesn't decide to build another on his own.
The only difference between gas and propane kilns is the burner. For propane you need a larger diaphragm. That simple. So when I discuss them, you can assume the same goes for either one with the above exception.
Again, gas kilns come in a good number of sizes, but the general shape should be square to slightly off square. I have seen large rectangular ones, but the problem of inconsistent firings and temps inside the kiln during individual firings. Best to stick with a square design..
With regards to gas kilns, you have to decide if you want an updraft or down draft kiln. Mine is an updraft. This is the most common type. It is not as efficient as a downdraft kiln, but you get a much more consistent firing with updraft.. Another nice feature of a gas kiln is that you can do reduction firing. That is what I focused on during my production days. I like the effects of a good reduction glaze(whether it be a copper red or a Chinese Temmaku or Celadon. This is the true essence of natural fuel firings. Electric kilns only produce an oxidized atmosphere. You can create an artificial reduced atmosphere by lifting the lid during the mature temperature and throwing in Epsom salts or other salts, but it creates very toxic fumes, destroys the kiln and really pisses off the Ceramics instructor<G>
Construction of a gas kiln is not "hard" but it does take a certain amount of forethought, and you have to pay close attention to the burner lay out amongst other things while building it. Best to do it right other wise you have to live with a kiln with a crappy design, inefficient firings as well as inconsistent. If you haven't figured it out yet, control and consistency will be your best friend for using it during glaze firings!
You will need two different types of bricks. Insulating bricks and fire bricks. Fire bricks are the heavy ones while insulating bricks are the extremely light ones that you can cut with a regular hack saw. Insulating bricks are the ones exposed to the fire inside and then the fire bricks are outside of that. Also there are a number of materials that you can put outside the fire bricks to keep the outside frame from getting too hot to be around, also, the more insulation you have the cheaper it is to fire :). I have seen and built kilns using only insulating bricks and an insulating fabric around that. I use to build kilns around pieces of sculpture that I would only do a "once firing" and didn't want to risk moving.
Next thing that has been done for a number of reasons are "shuttle kilns. These are just what the name implies and are usually used for production potteries. It makes loading and unloading a much easier chore. The shuttle is on wheels and there are rails it rides on leading to the kiln shell. The door is attached to the car so when you roll it into the shell, it seals itself. These some times look like train box cars in a train yard- it has long been a dream of mine to have a large studio where I have several "cars" and a nice pattern of tracks all around me<G> I think it would be neat as well as much easier for me to build my sculpture right on the floor of the car and simple roll it into the kiln. Also, I could have a car or two for my production ware and just fill it as I go. Being a one man production team it is hardly the efficient way to do things, but if I was Bill Gates, that is what I would do :)
Other types of natural fuel kilns include deasil fuel, coal and wood Kilns.
Of these, the wood burning kiln is the most popular.. they are just what they say they are and depending on what size kiln you have and how high you are planning on firing, you can go through a cord of wood for one firing. They are also some times called bank kilns. Simply because in ancient China, these kilns were built into a bank of earth. This would help insulate and keep the costs of material down. But not all wood kilns are bank kilns.
The design of a wood kiln is much different than the conventional gas kilns. You have a stoke box where the wood is fed into and heat rises into the kiln. And some times there will be two or more chambers going up a hill for these kilns. The upper chamber(s) usually contain greenware and only reach bisque temperatures while the lower chamber contains the pieces intended to be glazed. I have only limited experience with wood kilns so I will leave it there as merely a brief summary.
The last type of kiln I will describe is probably my favorite of all.
RAKU kilns
If you are not familiar with Raku pottery(I once has a cat named Raku- now I have one named Temmaku - he's about 10 feet away from me eating right now :))) Raku pottery was developed back in I believe the 13th century(I might be off by a mile, it's been that many years and I can't find my old college text book) by the Japanese for use during their "Tea Ceremonies". It is said to capture the true essence of live in the simplest use of the four basic elements necessary for pottery to exist: earth, air ,fire and water. <commentary> God how I miss this. Okay, sorry about that. Let me continue.
Raku kilns these days are very easy to make. I have one sitting out behind my barn that is nothing more than a 55 gallon barrel cut in half and lined with Kawool®. this is so beautiful. You put the burner underneath inside and open the barrel that has hinges welded to each half(actually, more like 70/30 or 60/40, the smaller part being the top.
A small hole(about 9" round is cut in the top of the barrel lid so you can see through and tell when the glaze has matured. It will look like suspended water but is actually melted glass/glaze.
You glaze your piece right there and stick it in the already heated kiln and bring it back to temperature. Once at temperature, it is removed using tongs and placed in a hole or tin garbage can. Both or either are filled with combustible materials such as leaves, wood chips, saw dust or ripped up news paper. Once inside, it is covered and this is the reduction part of the firing process. This is where the magic takes place. While still at a molten temperature The oxides, carbonates and other chemicals in the glaze are searching for oxygen to burn. In essence you are suffocating them and they in turn reach into their selves and burn off what oxygen might be contained in the chemicals.. The results are a stunning array of metallic colors or smoked whites, and or anything else is possible. It is so simple yet so magically beautiful, the Japanese and later Chinese, and now Americans hold raku pottery amongst the most spiritual thing you can do with clay.
We use to have raku firing parties way back when. A number of us would take the kiln(s) to a near by lake or woods bring our already bisqued ware, a couple tanks of propane, and our favorite legal beverages. We would some times do this beginning in the morning, and it was not unheard of to have a weekend raku party.
Okay, I think I'm out of wind right now. I'm sure there are mistakes contained in the above, and as I find them I will correct myself. Also, I had to leave out the finer details of construction and process as I do o not think your intentions here are to read a book :).
Hope this gets the ball rolling for you and I hope we can discuss things in future posts that may go into further detail as you move along building your kiln.
P.S> thanks again for the opportunity to share something I hold very dearly. |
