“speriamo stia su”: a wood kiln on Mt Bisalta
Last summer on Mt Bisalta we constructed a wood kiln, inspired by anagamas or single-chamber kilns built on a slope and without separation between firebox and main chamber.
The project started as a small hole in the ground for a pit-fire but quickly developed, in the span of a few hours, to an hypothetical cave-kiln directly dug into the earth banks or with an arch entirely formed in local earth. In the following days we learnt that we unfortunately needed bricks with the type of earth available locally and decided to plan the kiln more carefully.
I initially wanted to build a kiln similar to an anagama because of a few reasons: I almost only make unglazed ware which is what they were traditionally designed for, I wanted a kiln designed for long and dry firings, I enjoy their temperamental and somewhat inefficient style and I wanted to visually monitor the firing process, as it is the most straightforward way I have to understand what I am doing. I also find anagamas aesthetically pleasant as an object in themselves, they resemble and sometimes are just simple, unpretentious, honest tunnels dug in the earth. They are also diametrically opposed in philosophy of firing and building to the quick and efficient rectangular boxes I really do not like.
When I started the project I had a few things I wanted to achieve:
Building it completely on my own
Spending less than 1000 euro
Using 100% local materials
Finishing it in two weeks
Of course none of these were achieved.
I didn’t build the kiln on my own, thankfully.
Jean provided the land and also made most of the wood arch with bamboo which took all the patience I don’t have. Burcu (@studio_5.44) came to the rescue, and basically made every single brick of the kiln. We also fed each other energy and optimism when one was doubting the project and hesitation when being too optimistic, which was very good to balance the energy swings.
(Burcu and Jean almost never appear in photos because they don’t like to be photographed, but they do exist).The final budget was closer to 2500€ (without including the kiln shelves).
All the front and back bricks, and all the mortar and plaster are made with local earth and some silica sand stolen from a nearby quarry, but the upper portion of the arch was made with bought refractory alumina bricks.
It took five weeks and then months of doing the final touches, which to be honest are not completely finished yet.
The kiln was structurally completed at the end of summer and has already been fired three times. The plan is to have seasonal firings for a couple of years, then destroy it, recover the bricks and build another kiln somewhere else.
The kiln could have not been built without Jean, Burcu and also Michio Furutani, and his book “Anagama: Building Kilns and Firing”. I took immense inspiration from his style of anagamas and many technical tips.
We had to continuously make changes to the initial plans, and the kiln came out differently from both what I imagined and Furutani’s kilns, with another style of door and front wall, a quicker but more improper way of building and securing the arch, a “weird” sutema, a different bend of the arch, and overall different proportions from what Furutani suggests. While building the kiln we continuously asked ourselves what would Furutani do whenever we had a problem and we were reaching for his book whenever we had a question. His book occupied fully our mind and conversations for weeks.
I am not sure if he would agree, but I find his book not only incredibly generous, useful and interesting from a technical and artistic point of view, and an insight in his life stories, but also very pleasant to read for what seems to me like dry and cold humour that is really funny without even trying.
We started building the kiln before I read his book and was really happy when I saw that he suggests ideally positioning the kiln with a tall mountain in the north and a river in the south. “Speriamo stia su” gives his back to the top of Mt Bisalta and faces torrente Colla, which is just a few hundreds meters below to the south.
There’s a passage (page 197) in which he describes opening one of his kilns and finding it covered in insects which look like long legged crickets. They were a type of cave-crickets (kamadouma or “earth protectors”) in Japan and he waited for them to get out before starting the fire. The house where the kiln is has a basement that in autumn and winter is ofter covered in these big white cave-crickets. I felt it was a beautiful detail that I encountered the same insects in the place of the kiln and these small symbolic correspondences held a special place in my mind while we were building.
A special thanks also to Etna and Nyiragonga, who made the whole time building the kiln just su much better, giving us pauses to bring them on their obligatory daily walks, keeping us company at every stage of the build and reminding us to stop working just after sunset every day, their favourite time to run and wrestle around the kiln. They were an integral part of the kiln, almost literally as they fertilised all buckets of dug clay, and they now enjoy the firings as much as we do, as it means staying a few more days in the mountains.
The kiln site is in a grassy meadow in-between the chestnut woods on the hillside of Mt Bisalta (thanks Jean for allowing the kiln to exist for a bit!), a mountain that strongly characterises the nearby landscape. Its characteristic profile, with two close peaks (Bisalta means twice tall, bis-alta), is visible and recognizable from almost every point of the area of Cuneo. If you’d like to read more about the mountain, here’s a post describing some of her history, legends and clays.
We initially thought we could build the kiln entirely with local earth, by either digging a tunnel in an existing bank or by making the arch with thick slaps of earth. But given the qualities of the local material it wasn’t possible and we decided to buy bricks for the upper part of the arch, while using local bricks for the front and back of the kiln and have the floor and lateral walls simply dug in the soil.
We didn’t choose the best or most efficient way to do a process, or the best tools and materials, but what was available. This was a choice in order to save money and also because I believe it’s much more interesting to just work around problems and rethink of solutions.
The feet of Mt Bisalta are, from a material point of view, a really great location to build a wood kiln, and part of the choice on why we decided to build it here. Looking at the granulometry, the soil is mostly clay, which is good to dig the vertical and compact walls of the kiln, but also has a good amount of silt and sand that makes it less prone to drastic reduction of volume and cracking when fired. Because of the acidic nature of the mountain rocks, the resulting clay at the bottom is rich in silica and can perfectly sustain temperatures of 1250-1270C. It can also go a little above that without any signs of melting, but its density starts to decrease at around 1300C which is not good for a kiln and its structural walls.
A nearby sand mine, which is still in use, provided more quartz sand to reinforce the bricks and for the floors too.
We started simultaneously making bricks for the front and back of the kiln and digging the floors and lateral walls. For the bricks we had a mould in which we were just slapping local earth with a little added sand, and we were firing them in a small chimney built “for the occasion” just next to the kiln, which we called “Fumino”. This doesn’t make very strong bricks, as the firings were cold and short but it made strong enough bricks to be handled with care and be put in place.
We haven’t counted the bricks we made but it was the most laborious and time consuming activity of all the built, and took several weeks.
Together with us, there was one particular mud dauber which was constructing her nest at the same time, and kept coming to harvest mud on our fresh bricks. She was carefully choosing the best wet surface where to take her balls of clay and we decided to place one of her bricks, entirely covered by her marks, in the front.
The digging of the floor, layout and ash pit was done in just a couple of days. At that point we were convinced that the hardest part of the job was done and we were very wrong. We still hadn’t encountered the 8 kgs each bricks bought from Verzuolo or the broken wheel-barrel to take up hill or the bamboo.
The most technically difficult part was definitely building the wood arch. We used bamboo which grows just next to the kiln and some bought thin wood sheets to cover it. I don’t particularly enjoy working with wood and it took me a few days just to understand how to properly bend the bamboo. Bending and fixing the wood arch is what will make me think carefully about building another kiln in the future. It will need to be one of those rare times in which I am in an extremely good mood.
After building and securing the bamboo arch we started laying the bricks, which was fun. The construction of a kiln really just resembles that of any structure built with bricks or rocks, and I was lucky that my grandfather, who was a builder, taught me how to handle a trowel and mortar. He would have really enjoyed building a kiln.
The mortar was local earth with some added sand. For the arch mortar we sieved the earth, for everything else we didn’t bother as it was too time consuming.
We “fixed” each layer of bricks with broken triangular shards of refractory pots and shelves.
The arch was finished with a thick layer of plaster, mainly to homogenise the patchwork of different bricks of various lenghts and sizes in the endou, as for the smoke channel we used various second hand bricks. We also kept building up the chimney.
The chimney only has a passive damper. I wanted a simple kiln in order to better understand what for me are the important variables of a firing (size of fire mouth according to weather and season conditions, stacking rhythm and type of fuel) and I decided against adding 200 different dampers and unnecessary gadgets.
When all the construction was completed and the mortar and plaster had dried enough, we filled the chamber with leaves and offcuts of bamboo and set the arch on fire. There we had the first sign that the slope and chimney were pulling well, with almost no backfire even with an incomplete chimney and completely open front door.
The front area was dug to create a few small sitting steps and it’s quite uncomfortable with no proper rain protection, but very charming. We use a plastic sheet hanged in between trees to cover the kiln and ourselves when it rains or snows (thankfully we had Stela for climbing and swinging the rope!). Etna is the only one who enjoys this horrible blue plastic sheet cover, as he uses it as a slide.
Because the place gets a lot of snow in winter it would have been better to have a proper roof to protect the kiln, but since it’s a temporary kiln just a sheet of plastic is fine.
These considerations on temporariness of the kiln and the presence of snow affected also how we thought about the chimney, which had to be short and easily covered. The slope of the kiln isn’t quite enough to not have a chimney at all and at high altitude you need to pay extra attention to the pull of the kiln as there is less oxygen in the air. With bricks we reached just a certain elegant height which needed more, so we decided to hug the brick structure with two metal sheets fixed with wire. We put them on before every firing. I would like to say that the choice of adding the metal sheets to exactly this height is a consequence of careful and elaborate calculations but it’s not, I mostly wanted a tall tacky chimney to make high and flashy cones of flames out of it, all while exclaiming awe and contempt, just like any average man would.
The total cost came up to 2529€, basically the cost of around 2 to 3 firings in a kiln of someone else in Italy, or many places in southern Europe, but with the additional advantage of not having to spend time with the usual arrogant male potter that owns most wood kilns in this geographical area situated between “I spent 200k on a kiln that looks like an airspace but doesn’t fly” and “have you tried solving all your problems with heavy reduction”. I am glad that there is a growing amount of kilns owned by arrogant women as well.
Almost all of the budget was spent on bricks, some second hand, some new but second choice, some hard and some soft. The other expenses were ceramic fibre to insulate the arch (in hindsight this wasn’t necessary), some thin wood for the arch and a few hand tools we were missing.
It would have been better to start collecting bricks from second hand sellers and accumulate them for some time, but we didn’t have storage and decided to build this kiln quite spontaneously. It could have been done even cheaper though with more time and storage space.
This kiln was designed with dry firings in mind, and so far we have been thinking at how to best achieve that.
We have fired the kiln three times so far. I have discovered that I enjoy firing without a pyrometer and just looking at the conditions in the kiln and the cones in the front. But I guess it will take many more firings to be more relaxed about it.
Raising the temperature in the kiln seems particularly easy, almost excessively, which is a risk as the local materials shouldn’t go above 1270/1280 degrees. This is probably due to several factors, which I assume are:
the presence of a sutema,
the floor of the kiln and lateral walls being made in local earth, which has a high rate of reflection and radiation of heat, especially compared to the bought bricks. The bottom shelves, contrary to what should happen, have been hotter in every firing,
using the wood lid method above 900 degrees, which means a regular and heavy rhythm of stocking (so far, we have built a slightly too large firemouth for the proportions of the kiln, it should be made smaller),
using only pine as fuel for the part in which you need to aggressively raise the temperature. This comes from discarded planks and off-cuts from Segheria Pedona. Softwood like pine has more heat value compared to hardwoods and burns faster with longer flames, which means easier raising of temperature.
The greatest difficulty in firing anagama kilns is apparently the temperature difference between the front area near the fire, and the space in the back of the kiln, but I think that this can also be used as an advantage, carefully choosing what to load in the front and what in the back, especially for those who have several types of clay body that like different temperatures, as most working with wild clay do. So far we are having a difference of around 60 degrees from the firebox to the entrance of the sutema.
At times we have achieved quite nice flashing effects. We are keeping the firings quite short, trying to avoid going above cone 9 (not always successfully) and experimenting with an initial phase of crash cooling. I guess flashing works quite well in this kiln because the down part of the kiln is entirely made of earth, it has a tall arch and a slightly more elongated shape, an ash pit to reduce ash distributed on the pots and it’s located in a highly humid environment.
The flashing Furutani describes is different from what seems to be the common western understanding of flashing: for him it cannot have any build up of ashes, it tends to happen in shorter and colder firings, it depends on soluble salts present in the clay and it’s mostly done in oxidation, with a phase of crash cooling initially and then slow cooling. I am not that interested in understanding and assuming the particular chemistry of the particular type of iron salts that produce this and that effect, and their percentage in the clay body, as working with wild materials means I never know what actually is inside the clay I’ve collected. All samples collected in nature are complex cocktails that can have very different chemical makeup just a few meters from each other. I also constantly have new and different clay bodies.
But, from what I’ve noticed so far, in the very numerous three firings that I did in this kiln, what seems to matter most is the type of clay, primary clays being better than more plastic clays, not washing the clay (to not remove the solubles), and stacking and position in the kiln.
For this reason, I’d really like to spend more time loading without any urgency. I think it’s the most important thing to do.
At a point I’d also like to experiment with lengthening the firing schedule and waiting more before reaching top temperature, to see if it’s possible to do other types of firings and achieve proper ash effects in this kiln.
I have to admit that I enjoyed building “speriamo stia su” even more than firing it.
I got to spend so much time outside, with Jean, Burcu and the cats. I got to eat chocolate bignole from Pasticceria Dolce Idea at every big achievement of the kiln, so basically daily. And I got to build a really cool structure, for both what it does and what it is. I treated it very similarly to how I would treat a clay and vessel I care about and I enjoyed finding solutions and adapting the original plans to the specificity of the context.
It has thought me a lot about what I will do differently next time and gave me a bunch of ideas to try in the future. It has also impressively rested my mind and gave me a sixpack, which is already gone.
There are a lot of books on wood kilns and wood firing, I would really recommend these two to anyone wanting to delve more into it:
Furutani Michio, Anagama: Building Kilns and Firing, 1994
The book is available to purchase online.
Pdf copy of the translationHenrik Norsker, The Self-Reliant Potter – Refractories and Kilns, 1987
Pdf available here
