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    Gotheborg.com

    What sort of pigments are used in the glazes?

    I've been writing a paper on Chinese porcelain as I find it one of great interest. I have a question to which I have not found the answer, and I thought you may know: What sort of pigments are used in the glazes? I know that cobalt is used extensively for the blue, iron for the brown and copper for the red, but what about the pink, yellow, green, aubergine and black (and any other colors I may have left out)? I would greatly appreciate an answer to this, if you can find one.


    An outline of ceramic glaze colors

    I can't give you a full answer to this question since I don't have it. But, I will try to give you an outline of the principles anyway. First of all I think we need to consider that there are no "pigments" at all involved in ceramic glazes. The word is wrong even if I understand what you mean. What we need to talk about ar colorants or in this case - metallic oxides.

    To give you an example - common rust, for example - is red. This is because the oxide of iron is - rust, and it is red. Iron gets rusty because of air getting at it. Then air (oxygen) mixes with the iron and you get rust.

    If you could make rust go back to clean iron again, then it would go back to being black or blue again. This is the principle on how different oxides are used to color different enamels (melted glass) and glazes (melted stone). And we can regulate how this happens in a glaze by regulating the fire used to melt and fire the ceramics.

    So, lets go into this. Regarding colors, first you have to consider there are at least two kinds of glazes used. First of all - ordinary stoneware glazes such as Celadon and secondly all the over-glaze enamels used on Famille Rose and all the other kinds of enameled decorations, which are all pigments (oxides) mixed with - I believe - lead and some kind of other stuff (fluxes) to make them melt.

    To understand ceramic coloring, you need to have a mental picture of what oxidation and reduction is. This is the same as the difference between pure iron and rust, the latter being oxidized iron. To turn rust back to pure iron you will have to "reduce" it.

    This both could be done by fire. If you fire the piece with "more air than necessary", or with "less air than necessary" for the fire to burn properly.

    You could judge how this is going by looking at the smoke from the fire in the kiln. If there is too little oxygen inside there will be a lot of smoke.

    The reason I explain this is that you can actually get very different colors from the same minerals - or metallic oxides.

    Now lets think about iron and oxygen. It is oxygen that makes iron rust, or - oxidize.

    If you fire a piece decorated with iron in "too much" air the iron will oxidize and turn yellow, brown or red depending on concentration.

    If you fire iron in "too little" air the fire will "soak up" oxygen from the iron and leave pure metallic iron. Depending on how much iron and tiny amounts of minerals that happen to be present you will get wildly different hues of gray, green, bluish or black.

    Yellow, brown, black, red, grayish green (Celadon) was all made of iron. The same way as with iron, copper was used to produce both pink, red and green hues. Arsenic was used to produce white and Manganese was used to produce an aubergine purple.

    To make the black glaze on Famille Noire a green glaze was put on top of brown. Later I think they figured out a way to make black in one glaze. How, I don't know.

    Finally, the best kept secret in Chinese porcelain is how to make perfect red glazes. They did use copper, that on a bad day turned green or gray, but exactly how the went about creating perfect examples, I think that will remain a secret.

    Where would the magic of Chinese porcelain go if we knew everything?

    On my site there is a section called "Letters of Père d'Entrecolles 1712 and 1722. This is the best ancient paper we have on this. You can read those two letters if you are really interested.

    Best regards,
    Jan-Erik Nilsson

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