1 May 2013

IS IT WORTH THE TROUBLE TO MAKE YOUR OWN COLOURS?

Parmigianino, An Assistant Grinding Colours
Anyone who works with colours, especially on earthenware, knows that reds and yellows are the most difficult.You usually have buy them as commercial stains.  These are designed to be stable and so they don't have the qualities that studio potters look for, reacting with glaze, showing variation and creating texture. I prefer to use the common oxides, cobalt, copper, iron and manganese, rather than industrial colours - but I do like red and yellow!

The old maiolica potters couldn't get a true red, but they got a lovely yellow from lead antimoniate, a rich egg-yolk colour that we know as Naples yellow.  It has qualities unlike any commercial stain but you won't find it in the catalogues of potters' suppliers because it's so toxic. Naples yellow is, however, used by painters and it's available from L. Cornelissen & Son, the old-established artists' colourmen near the British Museum in London.  I've  tried it and it works, but it's expensive at £60 a kilo. (For comparison, iron oxide, which tin-glaze potters use as a brown stain, costs about £2.50 a kilo.)  So I made it in the studio.

The recipe I used was:
Red lead (Litharge PbO) - 60%
Antimony trioxide - 20%
Tin oxide - 20%
Calcine at 950 degrees C, grind and sieve through 200 mesh.

It costs about £10 a kilo but I've decided that it's not worth the trouble. A kilo would last me three years, so I'd be saving about £17 a year. First, the material takes time to prepare - a long time to grind and sieve - and crucibles have to be made for calcining. Second, there are the safety precautions that you have to take with such poisonous materials. I always bear in mind what Professor Nigel Wood told us in our first ceramic lecture at the University of Westminster, "Everything you use in pottery will kill you if you don't use it properly."  Lead antimoniate must not be swallowed, breathed in or allowed to come into contact with the skin even in small quantities, so you must wear gloves and a high-quality dust mask.  Those builders' masks made of paper will not do - I use a Moldex mask. Bench, tools and equipment have to be washed scrupulously after making. The washings cannot  be flushed down the sink: everything must be washed into a receptacle, waste allowed to settle, clear water poured off and solids melted into a glass before being disposed of. Any rags used for wiping up must also be disposed of safely and not simply put in the dustbin. During calcining, the studio has to be vacated in case of noxious fumes. There comes a time in your life when you realise what shops were invented for.
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