Beth Coe Maeda

"A alquimia permite criar jóias com argila, como faziam os egípcios.
É aí que o forno torna-se parte do universo onde o tempo é ignorado,
o fogo ainda é o mesmo e a magia do vidro se processa da mesma forma.
Com intensidade e energia o ceramista traz das cinzas o brilho e a poesia das cores,
transmitindo seu profundo amor à natureza."

Beth - February de 2008

Ashes glaze


The fire was a source of light and heat. Useful to cook the foods. It was when the primitive man discovered that, when taking certain materials to fire they became other things. The earth could become stone! Then came the ceramic.

The Egyptians were the first ones to have glazed ceramic; the source of their desertic lands gave their pieces and bills a turquoise color. With heir egyptian paste, where soluble sodium salts migrated to the surface of the piece during the drying, they obtained after the firing a glazing that imitated the stone they used in their jewels. With their techniques they saw that when mixing minerals with copper in their clay, they obtained shiny glazes, blue and turquoise.

Later, they discovered that using the same materials of the egyptian paste, they could make a glaze to be applied in the surface of their ceramic, resulting in a better application control, colors and effects. Even with highly alkaline and difficult application glazes, the Egyptians reached the 1050ºC in their firings.

Syrian and babylonians learned how to use the lead in their glazes and to color them with iron, copper and manganese. The lead already solved great resistance problems.

The Chinese primitive ceramic were also glazed with lead, but it was with the high temperature they obtained a better quality glaze. With the improvement of the kilns, by the chinese, 1220ºC were already reached. In that temperature the glazes were perfect, without splitting, without loosening of the ceramic and more resistant.

Totally by accident, the ashes started to be part of ceramic pieces. They discovered that the remains of the wood used as fuel in the kiln flew and fell on the bricks and pieces during the firing. They reacted with the clay and produced a natural varnish, beautiful and expressive, only with the movement of the fire. When taking out the pieces from the kiln, a ceramist found this effect when he saw the soft shine that made the pieces waterproof.

When cooked with larger oxygenation pieces were yellowish, and with reduction they acquired greenish tones. The firing conditions, such as temperature, duration, kiln type and atmosphere plus the composition of ashes determined the results.

The kiln temperatures that used firewood were controlled for obtaining a natural glaze with the marks of fire and with the characteristics of ashes, what gives the ceramic a simple charm. The wood ashes bring very beautiful effects to the glazes, like dark lines and grooves, in a rich texture result. For centuries the ash was used as melter in high temperature.

The pleasure in working using glazes with ashes is the possibility of trying to reproduce an old technique using materials easily found in nature. Without a firewood kiln, ashes are used in the glaze. In the past it was easier to obtain ashes, because firewood was very used, but that does not keep us from trying.

The use of ashes of wood or plants as ingredient in glazes makes its chemical composition variable, according to the part, origin and age of the used tree. A great amount of leaves or wood results in a small portion of ashes and consequent glaze amount. Some glazes are made with up to 50% of them.

Although basic, the knowledge of the raw materials used and the chemical reactions responsible for the formation of the glazes would be interesting. Using the materials appropriately, the chances of reaching the wanted result are much bigger, which translates into economy of time and work.

The ashes can be washed. Only tests will prove if there is any difference between using them washed or not. f the result is similar, then it's possible that the wash is not worth. The process is simple but it involves some work.

It consists in leaving them dipped in water - after mixing well - so that they decant. Never mix the dipped ashes with the hands. The use of rubber gloves is necessary, because the solution is quite caustic. The water with the dirts that migrate to the surface are removed and the procedure is repeated a few times.

The ashes can be dried on plaster or newspaper leaves. When dry they can be sieved and they will be ready to be used. (beware with the drafts, because the ashes are still corrosive).

The refractiveness (hardness) of the ashes depends on its chemical composition. If there's a lot of silica and alumina then they will have a higher fusion point. The rice peel ashes for example, are very hard (refractive) because they have an average of 75% of silica and around 9% of alumina.

The pine tree produces one of the ashes with the highest rate of iron. Seashells ashes can be used, that should be calcinated at about 1000 celsium degrees, inside a cooked ceramic pot. After being sieved they are used as a funding agent in the recipes.

The glazes with ashes will present differences in the final aspect, such as texture and color, modifying itself, for example the application layer or the firing atmosphere, if oxidation or reduction. The glazes with ashes tend to slip, the cares regarding the kiln shelves should be taken, such as a good kaolin and alumina application.

Burning the banana tree leaves
Attention to the excessive smoke
Rice peels
Cedar flowers
Used coffee filters
Embaúba flowers and leaves
Egg shells
Calcinating bone flour
Several ashes for tests
Embaúba flowers
Burning coffee filters
Cedar flowrs becoming ashes