Clay chimineas have real character. Some designs are made by hand rather than moulded, which means every one is slightly different. And the firing process means every clay chim, no matter how it’s made, has its own unique finish. How are they made?
How clay chimineas are made
In the old days clay chims were made from local clay, found in abundance in Mexico where chimineas originated. The clay was brittle, but fixing a broken chim was relatively easy. All you did was grab a handful of sticky stuff from the nearest clay pit or stream bed and stick it on to form a seal. These days modern chimineas are usually made from red clay, rich in iron and much the same as the stuff used to make terracotta plant pots.
What is clay?
Clays are fine natural muds used to make pottery, the raw materials for pots of every kind. Everything from low-fired terracotta plant pots made from coarse, iron-rich red clay to coarse or smooth grey clay with no iron, used to make things like microwave-safe mugs and crockery.
The very finest ceramics are made from delicate, high-fired porcelain clay, the best of which you can actually see through, often called bone china. As a general rule, the higher the firing temperature, the harder the resulting pottery.
When it’s being fired in a kiln, thinner chunks of pottery fire faster than thick ones. That’s why so many clay chims are made in two pieces, the body and the chimney itself, which are fused together later.
Preparing the clay
To make a chim or anything else from clay, you first need to manipulate the clay to get rid of any trapped air. Air heats up and expands inside clay, which is why the end of a firing can often deliver nothing more than a kiln full of broken pots. A potter preparing clay by hand will slam it onto a smooth work surface, knead it, tear it in half then smoosh the halves together, then repeat the process all over again, several times.
Throwing a chim on a potter’s wheel
You can ‘throw’ a chiminea on a potter’s wheel if you’re skilled enough, something that takes years of practice. Centrifugal forces mean it’s a challenge to throw something so big all in one piece, although a highly experienced potter will be able to handle it. Someone less experienced would throw a chim in two halves then stick them together with slurry – diluted liquid clay – once the halves have dried leather-hard.
Building a moulded or coiled chiminea
Make a plaster mould, mix clay with water to form a slip or slurry, pour it into the mould and the plaster sucks all the water out of the clay mix to leave an even layer. Break the mould before the clay dries, when it’s leather-hard, and voilà, you have a beautiful chim. You can also make a chiminea by coiling long, thick worms of clay round and round to form a coil pot, the outer and inner surface of which you can make smooth before the clay dries.
What does firing clay involve?
Take one freshly-made clay chim. You can’t fire it until it’s completely dry, otherwise fast-expanding water in the clay will cause cracks or even explosions. Your first firing is called the bisque firing, which hardens the clay into actual rock in exactly the same way as volcanic activity and high pressure transform mud into slate. It takes hours, and temperatures rise as high as 1200 degrees.
If your chim is glazed, that happens at the second firing. The glaze – usually something to provide colour mixed with clay and water so you can paint it on – is applied to the bisque-fired body, which is put back in the kiln to heat the glaze until it melts to provide the required colour.
Glazes come in many forms, from highly colourful man-made chemical glazes in powder form to hand-made glazes made from natural materials like wood ash. Traditional Japanese Tenmoku glaze, for example, is rich in iron crystals that create a lovely, deep brown, purple, yellow or black shiny finish, depending on how you fire it. Yohen is a natural ash glaze, and others are made from powdered glass.
How small can a chim go?
If you’re fortunate enough to have access to a pottery studio and kiln, or you take pottery classes, you don’t have to challenge yourself to make a full-size, garden-size chiminea. Try making a mini-chim and see how it goes.
Air dried and kiln dried chims
A clay chiminea will usually be either kiln dried, ie. Treated, or air dried ie. untreated. Kiln dried chimineas are usually pre-painted and sealed, ready for use. But air dried chimineas have to be painted and/or sealed first, before you use them.
How to move a clay chiminea without breaking it
With the best will in the world, the join between any two pieces of pottery, especially when they’re thick and heavy, represents a weak point. The best way to move a clay chiminea is to put one hand on the lip, where the bowl or mouth opens, and cradle the neck gently with your other arm.
Come back next time for more information, news, views and developments in the wonderful world of chimineas. Summer’s here, so the timing is perfect!