"A cerâmica é a expressão da arte onde os dedos executam a criação.
O ceramista, através das mãos, fará apenas parte da obra,
deixando à criterio do fogo a magia do toque final."
Beth - Fevereiro de 2008
These glazes appeared on China during the Sung dinasty (960 - 1279).
The discretion of colors, color depth, glass' melting ability and a very hard surface combined to a shiny translucent color, in high temperature, were already something special thousands of years ago, and they're stil not easy to replicate. It's a technique that gives ceramic a classy look.
The secret programmings of firing, glaze density, clay body to be used, will all influence the glass work, where the goals are: melting, depth and color.
Celadons are colored by the iron oxide, with fire being blast in reducting atmosphere, at high temperature. The transformation of ferric oxide into ferrous oxide gives the glaze the blue green color, which can also be yellow, in a scale that varies from olive green to gray.
The raw materials are grinded until they become a really thin powder. The raw materials lower on iron give lighter colors.
Oxidation and reduction firing::
The ceramic objects are heated to a certain temperature. The heated ceramic extracts the oxigen from the chamber, burner entrances and all holes, cracks and openings on the kiln.
Oxigen is combined to the glaze materials and the ceramic bodies. The glaze metals, like iron will oxidize, giving the glaze a particular color.
To an oxidation fire, just leave the kiln's air entrances open. These details refer to gas or wood kilns, which allow to do oxidation or reduction fires. Eletric kilns do oxidation fires naturally. Doing a reduction in an eletric kiln is possible, but requires skill and knowledge.
The kiln's air entrance is restrict, resulting in the saturation of the free carbon at the kiln's atmosphere, in major carbon dioxide and monoxide. The glaze metals like iron will suffer reduction, presenting different colors than in a oxidation fire. For example: a single glaze can be green in oxidation and red in reduction.
In a firing with string reduction the flames get to escape through the kiln's openings and cracks. This happens because it lacks oxigen inside the kiln and the fire will seek it wherever it can. Celadon is a typical reduction glaze.
My Celadon tests are still far from ideal, hence the results are still poor.
To correctly realize the glaze, I select the ones of better surface and color, adding missing things so that they get close to the examples I saw.