Jon Pacini on mon 23 jul 01
Alisa wrote--------"Talking about mold, makes me remember something I read a
long time ago on
Clayart.
The post said that green molds in clay are fine and add to plasticity,
etc. The black molds
are not all right because they can leave pock marks in the fired piece. I
can not remember
who wrote this, but wonder if it is true."
Greetings all------Black molds many times leach iron out of the claybodies
and concetrate it in pockets or on the outside surface. Not sure if the mold
starts out green and turns black because its changing red iron to black or
if the mold is naturally black.
When slab rolling or pressing the clay, these moldy areas will remain
dark after firing, provided you don't wedge them in or scrap them off. The
Wedging process seems to blend the clay all back together quite
sucsessfully.
Green molds don't seem to effect the fired color of clay.
Since these growths are primarily organic and if they were in
concentrated amounts, I can see where they could leave a void, pit or pock
in the clay when fired.
I get lots of requests for bleach to be added to combat molds. Seems to
run counter to the tales of moldy clay being the best to work with however.
Jon Pacini
Clay Manager
Laguna Clay Co
Martin Howard on tue 24 jul 01
Many may be mistaking mosses and liverworts as green moulds.
They are different.
My 25 kg bags of earthenware clay grow both mosses and liverworts.
I haven't been aware of just moulds, but they are probably there as well.
The mosses and liverworts grow because there are some spores in the original
clay storage area or in the bags, or the bags become split and the spores
enter and grow in the humid condition there.
They would burn off in the kiln without any trouble at all, as far as I can
see.
Martin Howard
Webb's Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ
England
martin@webbscottage.co.uk
http://www.webbscottage.co.uk
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