Spring has been my favorite season for a long time, Daffodils are blooming, trees are budding, birds are chirping, the sun is shining and the weather is warming….and I don’t think it’s a coincidence that Spring is also when Raku returns. Although I do have fond memories of my dad firing in the winter time (one of his favourite things to do was quench the hot pots in a snow bank), it is the warmer months that are most common for outdoor firings. I think Raku firing is such a wonderful community event. Whether you’re an art teacher looking to do some fundraising for supplies, or an art center looking to build awareness of your program, or you just want to get to know your neighbors, there’s nothing like the excitement and interest generated by open flame. I wanted to write a little about Raku as a process rather than just the glazes for them.
Raku is where I first really caught the “pottery bug”. Of course, going back to my Girl Scout days, I’ve always been intrigued by and absolutely in awe of fire. I helped my Dad with the burn pile at home (and continued to burn the tree trimmings and brush for my mom after he died….MAN did I get some big bonfires!), and Independence day? Forget about it…you’ll have to fight me for the chance to blow anything up. Give it up and just enjoy the show. So, showing me a 100# propane tank and a burner capable of half a million BTUs and saying “ya’ wanna?” just made me twitch.
But as much as I love the fire, I also love science and experimentation, and I ask a LOT of questions. Eventually my mom said “I don’t know, Cindy, why don’t you try it and see….” I think that is an important thing for anyone considering or currently doing Raku to keep in mind. Don’t be afraid of it…Try new things. Raku firing is a process, a technique, a tradition, a style, but what is not, is a set of strictly-enforced rules. There’s not a wrong answer. HOWEVER, every time we have a Raku event, I do get a lot of questions, so I though it might be helpful to post some of those FAQs, and other various and sundry tips, tricks and other info to get you started:
To kick off this series of blog posts, I decided to start with what I think is the number one question I get asked the most is:
“How do you know when/how much to turn the burner up?” – This is also perhaps the most difficult question, because I don’t really think about it any more. It’s somewhat instinctive for me now. When I fire, I have a sense of the life and breath of the kiln itself. In time, (and perhaps in future raku education posts), you will come to understand this yourself. But don’t worry if you don’t know, because I, like most people, was also clueless when I fired my first kiln by myself. And yes, a little scared too. You certainly don’t need to be scared, because worst case scenario, the pieces don’t turn out the way you want and you re-fire them. More fire = more fun!!! BUT, if you feel you need a starting point, you can use the following schedule, but only if you PROMISE me that you’ll only use it for your first 3 firings. After that, strike out on your own and get to know your kiln….
- From a cold kiln, start with the burner on about as low as you can get it to produce a “lazy” flame that meanders into the kiln.
- Leave it at that for about 10 minutes. This is to gradually heat up the kiln, bricks, shelves and ware.
- Turn it up to about double that flame. You can either listen to the sound of the torch, look at the magnitude of the flame, or you can just turn the valve on the torch about a quarter to a half turn.
- Leave it at that for about 10 minutes
- Double it again and leave for 10 minutes. (Around now you should be noticing a bit of color in the kiln)
- increase the flame by about half (a quarter turn) and leave it for 10 minutes
- increase the flame by a quarter turn again and leave it for 5 minutes and repeat (during this time, check your reduction bins, gather your gloves and tongs etc.)
- at this point, you need to look at the glazes in the kiln. They should be frothy/bubbly/molten (you can kind of see this in the picture at the right).
- continue to turn the burner up at roughly 5 minute intervals until the glazes smooth out and are glossy.
- turn the burner off completely and (wearing gloves, of course) lift the kiln straight up and over the pieces, then set it to the side:
I also asked Dave for how he would explain it. He’s a bit of an over-achiever, and went into WAY more depth than I did, so rather than combine his and mine, I decided to just copy/paste his as well:
1) Light burner. Position the tip of the burner even with the outside wall of the kiln, and adjust the pin valve so that a small, lazy flame is all that is coming out of the burner. The flame will trickle its way under the kiln shelf, and the tip should *just* impact the target brick on the back side of the kiln. Wait about 10-15 min for the shelf, bricks, and pots to heat up. This will keep your shelf from cracking during the firing. **AT NO TIME DURING THE FIRING SHOULD THE FLAME IMPACT THE EDGE OF THE KILN SHELF DIRECTLY**
2) Take a look inside the kiln at the pots. If you can see areas of glaze that are still drying, keep waiting until the glazes have dried out completely in order to keep them from sloughing off during the firing.
3) Turn the burner up until you have a moderately strong flame that now solidly impacts the target brick. This turn-up should be about a 1/4 turn-up on the pin-valve. Pull the burner away from the kiln so that the tip of the burner is about 1-2″ from the kiln wall. Wait another 15 min.
4) Look in the kiln. The target brick should be glowing (and possibly the brick kiln pad as well). The glazes may be beginning to *sweat*, *weep* and/or bubble at this point. Copper matte or matte iron glazes will begin to turn black at this stage.
5) Turn the burner up another 1/4 turn on the pin valve. You will hear a significant increase in the volume and depth of the ‘roar’ of the burner. back the burner away from the kiln about another 1/2″. Wait another 10 min.
6) Look in the kiln. The glossy glazes should be solidly bubbling or frothing at this point, and there should be a solid bright orange glow from UNDER the kiln shelf.
7) Turn the burner up a bit more. This turn-up is NOT about how much to turn the burner up, but a matter of finesse. You shouldn’t turn the burner up an entire 1/4 turn at this point. Make small adjustments more frequently and wait 5 min or so between changes to let them have a noticeable effect. The object is to get the glazes to flatten back out, heal over all the bubble marks and, at the same time, raise the glow within the kiln to the top edges of the pots.
It should be noted that unless you are trying to reduce inside the kiln chamber during the firing, you shouldn’t see a lot of fire shooting out of the spy-holes. You want the propane to explode INSIDE the kiln (thereby driving the temperature upwards). If you do see more than 1″ of fire coming out of the spy holes, turn the burner down a little, and pull the burner tip about 1/2″ further away from the kiln (to allow more air to mix in).
8) When complete, the glossy glazes should look like a hot, wet lightbulb. The surfaces of the glazes should be smooth but NOT runny. At this point, you are ready to turn the burner off and proceed to whatever post-fire treatment you have chosen.
I do NOT use cones in raku for any reason simply because the firings are so fast that cones are no longer accurate. I also do not use pyrometers unless I am firing a glaze or a slip-resist technique that requires pretty specific temperatures. By observing what is going on in the kiln, you can accurately fire the glazes.
For subsequent firings, you may OMIT step 1, as the shelf and bricks will still be hot from the last firing.
If you still feel unsure, you might like to watch this video below that I created, or come to one of our Second Saturday Raku Events, like the one this Saturday, (April 12, 2014) and ask to learn! Dave and I are always happy to share our knowledge!