Feet of Clay

When firing a wood kiln, or salt or soda, one of the challenges is preventing the feet of the vessels from sticking to the shelves. In any of these firings the atmosphere in the kiln is full of glass making materials, either as fine particles of ash or gaseous sodium trying to flux any free silica in the clay to a liquid glaze. In fact, that is our objective, and by allowing this flow of glass making materials to wash over our vessels we invite nature to glaze and decorate our work for us. It is difficult to be selective, however, about where those gases or particles flow without sacrificing the spontaneity of the glaze effect on the whole vessel. If the liquid glass flows down to the foot of the vessel, then when it cools the foot will be stuck to the kiln shelf by solid glass. This is difficult to remove without chipping the piece or damaging the kiln shelf, and such losses can become quite expensive.

There are several ways of addressing this challenge and I employ two methods in my kiln, depending on where the pots are to be placed. The first is to try to prevent the pots from sticking. My first step in this process is to design my feet so that there is a minimum amount of surface area in contact with the kiln shelf. The foot ring itself is trimmed with a chamfer on each edge so that only a thinly angled line touches the shelf. This also creates a slight overhang to help prevent fly ash from getting under the foot. When the vessel is removed from the kiln the foot ring can be touched up with some sand paper and "Viola!", a nice smooth foot ring. When I am waxing the feet of some vessels before glazing, on plates for example, I use a special wax mixture of candle wax, kerosene and a handful of alumina powder. The wax burns off in the kiln, leaving a very fine residue of alumina between the vessel and the kiln shelf. Alumina (Al2O3) is a highly refractory material, the melting point of which is about 2040C, and so it remains as a dry powder even at glaze firing temperatures, and will serve the same purpose as flour on the work bench when you are making pastry or bread, preventing sticking. Following the same train of thought, Alumina is used as a coating on kiln shelves and kiln furniture to prevent sticking, just as flour is used on the inside of a cake tin. On its own, however, alumina floats around as a powder and can stick to glaze surfaces making them matte and unattractive, so a coating mixture containing some clay material as a fixative is necessary. The mixture which I use is Alumina 2: Kaolin 1 proportionately by weight, mixed with enough water to make is a pourable creamy consistency. I put this into a watering can and pour it over the surface of the kiln shelves, then put them out in the sun to dry. After every firing I scrape any accumulated ash or soda deposits off the kiln shelves, so that they are ready to be coated again for the next firing. It is important to use a dust mask and eye protection during this process! The materials are all non toxic, but inhaling dust can cause lung disease, and chips of broken glass in the eyes should be avoided at all costs!

My other approach to this challenge is to accept that a wood or soda firing is what it is. There is going to be ash and glass dripping of the pots, and it's going to leave marks. If you are trying to avoid that and it happens by accident it can leave nasty scars on the pots. If, however, you accept it and allow it to happen as a part of the total design, those marks become cicatrices, like tribal scars, and a beautiful expression of the firing process in the finished work.

I do not use wad mix directly on the clay, as that goes in the nasty scar basket. Instead I use a ball of fire clay, rolled in alumina, stuffed inside a sea shell. A set of three, or sometimes more, of these will form a stand on which the vessel can be placed, raising it off the kiln shelf. When the kiln is fired, the salt in the shell will volatilize off leaving flashing marks on the clay. The Calcium Carbonate (CaCO3) in the shell will lose Carbon Dioxide (CO2) and become Calcium Oxide (CaO), still retaining its original structure between the vessel and the fire clay. Any glaze, ash or soda will flow into the shell structure. When the vessel is removed from the kiln and placed in a bucket of water, the Calcium Oxide (Quick lime) will rehydrate to become Calcium Hydroxide (Ca(OH)2 or Slaked Lime), and will just wash off the vessel leaving a fossil like cicatrix where it was in contact with the surface. The slaked lime goes on the compost heap. A touch up of the sharp edges left on the glaze deposit with some sand paper, and Robert is your fathers brother! This is the method I use at the fire face, where the forces of nature are most energetic and capricious. I described this process and my feelings about it in my "Art for Eternity" entry, and I invite you to read that by all means. The greatest challenge for a potter, however, is knowing when to take control, and knowing when to surrender it. It is this balance, this dance with the elements, that creates such beauty, that gives great joy to the user of these vessels, and makes being a potter such a fulfilling career.

Merry Christmas!

Christmas has come once again, reminding us how important our family and loved ones are to us. This December we have spent a great deal of time going to doctors for Sean (4), who has been fighting pneumonia. Last week he was given a clear bill of health, only to have been diagnosed with Influenza today. We are praying that Santa Claus will bring him a quick recovery.







In the time between I have been trying to fill orders and have managed to deliver them in time for Christmas. Of course the kiln can't be fired unless it is completely full, so to fill the kiln I made these 300 beer cups as well as the orders.













Japan is not just the land of the rising sun, but also of the frequent earthquakes. Last Friday, just when the firing finished and the pots were still hot and sticky inside the kiln, we had two fairly large earthquakes here (the epicentre was the other side of Tokyo, but it was still significant here!). So, I waited with baited breath for the next few days for the kiln to cool enough to unpack it and assess the damage.

Thankfully we only lost two shelves of pots, and the four stacks supported each other in the kiln and the ash and glaze was just sticky enough to hold it all together! Stability is always an issue when I am designing my work, and I'm pleased to say that not a single cup in the whole kiln actually fell over!

In a situation like this it is important to remove as many pots as you can from the kiln before you disturb the shelves, just in case it all comes crashing down!



So, I am grateful for all my blessings, hopeful for a bright new year, and I pray for the health and happiness of all those I love.

I wish you all a blessed Christmas.

A Course in Basics

It is no accident that there is a similarity in form between thrown cylindrical pots and the structure of bamboo. Though they are not "Copies" of bamboo, a cylinder is a cylinder, and man made forms will naturally have commonalities with natural forms.









When learning to throw on the potters wheel the most basic skill one must master is the making of cylinders. All other forms thrown off the wheel head are based on this form. So, step one; Make one hundred cylinders.










It is important that they be accurate in size. These pots are 300 grams each, so if the weight of the clay is the same, and the height and diameter are the same, the wall thickness will also be the same. By turning the foot in a curve from the hip to a foot ring slightly smaller in diameter than the inside of the lip, the pots can be stacked for easy storage in the home or restaurant. The external rim measurement for these cylinders needs to be 72mm when fired, so allowance is made for shrinkage, which in my clay is exactly 10%, so the wet measurement was 80mm.
　　
　　
　　

And what are they for?

　　

　　

　　

They are lidded containers for another course of the Toyoda "Euan" menu which starts on September 30th. The lids are lacquer ware, and the pots are made to fit the lids, thus the diameter of the rim is vital. After 30 years of throwing, I still take great joy in making these simple forms. It reminds me that the key to mastering advanced skills is essentially the mastery of basic skills, of course.

ART FOR ETERNITY; Discovering "Nontemporary Art"

Twelve million years ago Japan was the bed of a cold and shallow sea. Volcanic action and the moving of continents pushed this archipelago up out of the sea, built mountain ranges and valleys. Rain and erosion resculpted the landscape, filling the valleys with clay. Vegetation created rich soil and over ages these islands became what they are today. Throughout Japan, however, there still remains a layer of sedimentary rock, a strata that was once sea bed, and the evidence of its history can still be found there. 　　

　　

　　

"Ichikai", the name of the town in which we live, means "City of Shells". In this area there are some of the best fossil deposits in Japan, and the other day we went excavating with some people from the prefectural museum of natural history. 　　　

　　

　　

　

　　

　　

　　

　　

　　

　　

　　

　　　

　　

　　

The children all participated, and we found a variety of different shells. 　　　

　　

　　

　　

　　

　　

　　

　　

　　

　　

　　

　　

　　

　　

　

　　

Time and pressure had changed the structure of the primordial mud, forcing the separate particles to meld together, embedding these beautiful forms and pattern into the rock for all eternity.　　

　

　　　　

As a potter, I too am trying to transform mud into stone, melting the particles together to form a new material which bears the patterns and forms which I have consciously created. By firing the kiln to 1300 Celsius I achieve in human time scales what nature does in geological time over millions of years. There is a limit to what I can do though, and I trust the forces nature to take my work beyond my limitations.　　　

　　

　　

To prevent the pots from being stuck in the kiln by liquid glass from the molten, running ash I will sometimes set the pots on sea shells. I fill them with clay to prevent them from collapsing, then place the pots on top of them.In the firing some carbon dioxide will burn off from the calcium carbonate of the shells, leaving the shape of the shells intact as calcium oxide. 　　

　　

　　

Even if ash runs down and sticks on the shells, the pots can be taken from the kiln with the shells attached. They can then be put into water and the calcium oxide will dissolve into sludge, leaving only the shell marks on the foot of the vessel, in this case tea bowls.
　　

　　

Sea shells also contain a small amount of salt, which will turn into sodium gas during the firing, giving orange flashing on the inside of the foot. The spiral left by the trimming tool on the base of the pots resonates with the spirals of sea shells, not as a conscious representation but as a natural consequence of the forming process. 　　

　　

　　　

It is the beauty which springs from the natural process that imbues these works with their intrinsic charm. This beauty, this art, is not pretentious nor contrived, like much representational art, nor is it bound to a specific set of aesthetics or social mores as is contemporary art and fashion. This beauty is relevant to any one who loves beauty regardless of culture or creed, in any age, and will last for all of eternity. This is "Nontemporary Art".

How I Stack My Kiln

There are many people who have now built my kiln, and everyone will stack and fire it differently in order to achieve their desired result. Just for the record though, I wanted to show you how I stack my kiln and why.

Firstly, The brick arrangement under the shelves is designed to force the flame to the front of the kiln. The surface area of the space between the bricks is equal to the surface area of the flame inlet mouths at the back of the kiln which also equals the exit flue in the floor off the kiln. That means that the same amount of flame can come into the kiln, find its way through the work and exit the kiln. draft can then be controlled by the damper and the stoking volume and rate.




The first layer of shelves goes onto the bag wall right up to the fire face. There is a coil of wadding along the bag wall to stop the draft going straight under the first shelf. It forces the flame to go up first without taking short cuts.









There is a gap of 13cm on either side of the shelves. The pots can overhang this gap as much as you like, it won't affect the firing. You will notice how crusty the kiln is; that's because I've fired it 120 times over the last 10 years.









Between the shelves I leave 1.5cm of space only, this is part of the total exit space calculation.












It is important to stack this kiln tight. How tight? Tight as a salmons sphincter should do it. I only leave one or two milimetres of space between pots. Firing raw means the pots will shrink away from each other anyway, but it is also important to stack as tight as possible because the kiln is built of insulating brick and doesn't store a heat mass, so the work must become the heat mass.





I try to get as many pots as possible into the kiln. These cups have no glaze on them at all, I am relying on the wood effects to glaze them for me, the best place for them is at the fire face. Glazed work should be stacked at the front of the kiln away from the direct flame.









The handles force me to leave more space above the pots than I would like. Ideally the space should be about 1cm.











I stack right up to the arch, keeping it as tight as possible. There is plenty of space between the pots for the flame to get through, and as it does it leaves ash and vapour flashing. If there is too much space around, above or between the pots, the flame will rush straight past the pots and up the chimney, taking all its ash and vapour with it.







The front shelves go in with the same 1.5cm gap.
A long brick bridges the gap over the flue.

The front stack is also stacked tightly, with work that I would prefer less ash on, like the black glaze, or pots that I want more red or orange flashing rather than ash deposit.

This firing only used 40 kiln shelves, but the maximum I have used is 80, all plates. The tighter it is stacked, the better. It usually holds about 400 pieces per firing.

Packing them in

The way a kiln is packed affects the finished outcome of the pots. The height of the shelves and the space between pots can be adjusted to control flame flow.

In this firing the shelves are close together towards the bottom and spaced wider at the top in order to force flame flow up the fire face rather than let it flow through the kiln lower down.

The pots are arranged also in alternating rows to make the flame travel diagonally through the stack. I have done this because I want to have stronger ash and flame effects on the pots at the back of the kiln which are mainly unglazed, and by so doing reduce the amount of ash that carries through to the front of the kiln where I have placed black glazed dinner plates.

The wine goblets have "Igusa" straw tied around the stems, any excess from which will fall into the "Kumidashi" tea cups which fit into the space between their stems.

Too much ash on the black glaze waters it down and turns it a honey colour. I try to keep the straw off the black glaze for the same reason, but want to have markings on the rim.

Pyrometric cones are placed top and bottom to measure the heat work inside the kiln. Made from the same materials as glazes, they will melt at set temperatures. I always put in cones for 1260, 1280 and 1300 degrees celsius.

The last thing to do is close the kiln door, which entails stacking about 200 bricks into the kiln mouth. To prevent grains of sand or dust from falling into the pots at the front of the kiln and spoiling the glaze, I dip the bricks into a tub of water as I stack the door. This also reduces the major health risk of dust in the air.

Once the door is stacked I seal the top with fire clay and it's ready to fire tomorrow.