Last summer, in August of 2014, I had the fantastic opportunity to participate in a series of what are sometimes called 'alternative firings'. In fact, looking at the dates, it was exactly a year ago, and that makes this post somewhat of an anniversary and homage to the experience.
To set the scene: picture a dozen potters and their dogs or significant others all gathered together at a lovely hilltop property. There's a small pond, plenty of land for tenting, and a summer home. Everything is green, cool, and peaceful. In one small corner of the land are a few kilns, a large hole dug in the ground, and some clamshell charcoal grills. We had all the necessary tools to have a weekend full of alternative firings - we would be exploring pit fire, raku, horsehair, and obvara. For the purposes of this post, I'll be talking strictly about what we called 'raku' firing, since it seems to be the most confusing, and the current use of the technique tends to stray from the original use.
If you look up 'raku definition' on Google, the most popular definition that comes up relates to the lead-glazed tea bowls used in the Japanese tea ceremony. Knowing what we know about lead, and what I will tell you about the temperature that raku generally fires to (not high enough to make it water-tight), you could probably think of this traditional definition as quite confusing, at best. From what I understand of the tea ceremony (not much - if anyone is an expert, feel free to correct me), the length of time the tea actually spent in the cup was not very long, so there wasn't time for the lead to leach into the tea, or for the tea to really absorb into the cup, causing brittleness and breakage.
In our modern, non-traditional times, raku fired pottery is never considered food-safe (although most raku glazes are now lead free), and only work that would be decorative or artistic should be glazed in this manner. I made a lot of vases and candle holders for this alternative firing weekend, because I can't stand the thought of a non-functional piece of pottery that I have made. For those of you that are thinking about the fact that these pieces are not watertight - there are ways to seal the inside so that the container can, in fact, hold water.
But moving on! Let's talk about the process of modern raku firing.
1. Make something. You've got to start with something. A vase, a decorative dish, a handbuilt animal.
2. Bisque fire the something. Bisque, or biscuit, firing is the first of two firings in making pottery. Your vase begins as some clay dust mixed with water. You make it into the shape of a vase, and then let it dry. Most of the water evaporates out at this point, and now you've made clay dust hold a shape, but it is very brittle and fragile at this step. To harden it, you must bisque fire the piece. This process squeezes the clay particles together and makes them harder by essentially baking the remainder of the water out of the piece. The result is that the trace elements in the clay morph and blend and merge together to create a much more solid, yet still absorbent, piece of clay.
3. Using a raku specific glaze or glaze formula, paint, spray, or dip your something to your desire. Ceramic glazes are essentially different chemical compounds, combined in different ratios, mixed with water. The fired result of the piece will depend on lots of factors - the ratio of aforementioned ingredients, what the ingredients are, how thickly the glaze is applied, in what manner the glaze is applied, the type of clay the glaze is being applied to, the shape and thickness of the piece, the temperature the kiln fires to, how quickly it fires.... I could go on, but you get the idea. The point is, there are a lot of factors involved in making this kind of work, and one only has a minute amount of control over each of them. This means that each raku fired piece is truly one of a kind - results are very hard to duplicate. Raku glazes are specially formulated to create drastic results based on the method of firing, which is:
4. Fire kiln to specified temperature (our ideal kiln temperature goal was about 1800ºF), remove red hot pieces (very carefully) with tongs and proper heat shielding gloves and heat resistant clothing, place in a bed of shredded paper and cover with more shredded paper until the piece catches the paper on fire. Let burn for a handful of seconds, then cover completely with metal cover (trash can, barbecue lid). This is what we used the clamshell barbecues for - the bottoms were filled with shredded paper, and then more was tossed on top of pieces as they were added to the firing chambers. Once covered, the chemicals in the glaze have alternating reactions with the extreme heat, the drastic temperature drop, and the subsequent burning away of oxygen into carbon. I don't know the exact science, but it ends up looking pretty cool.
5. After a certain amount of time (perhaps 15 minutes or so?) remove the still warm pieces from their bed of shredded paper with heat resistant gloves and place to completely cool on a heat resistant surface. The fire needs time to burn down, and opening the lid of the chamber too soon could cause a different final product. You can see in the pictures below that we used a series of bricks stacked along the ground as our cooling area.
As I mentioned earlier in the post, there are ways to seal the inside of raku pieces to make them watertight. Since the ideal raku temperature isn't hot enough to vitrify the clay, I used a water sealant designed for concrete, brick, and terra cotta. All of the raku (and horsehair, obvara, and pit fire) works in the shop are absolutely watertight, so they're great for live flower displays. Now that you know more about the process of raku, you can brag about how your raku vase is one of a kind, and you can describe the numerous steps involved in the making of it.
Next time we'll talk about horsehair and obvara, two other firing techniques we used over this lovely August weekend one year ago.