Peter Grieve on tue 29 jun 04
Hello all,
I am trying to duplicate various British Georgian soft paste
porcelain bodies. Using rational analysis on a Sevres soft paste formula
given in "Treatise on the Ceramic Industries" by Bourry, a stab at the
glassy body might be:
10% Ball Clay (White firing)
65% Ferro 3110
25% Whiting
Obviously this will not be a very plastic body. Nor will I be able to fire
it to full vitrification, since it would then be a liquid pool on the kiln
shelf. Both of these traits are in line with soft paste characteristics.
A more usable (but I think less accurate) soft paste reproduction might be:
25% Ball clay
10% Kaolin
65% Ferro 3110
20% Whiting
And Susan Peterson's book gives a cone 04 glassy body
25% Ball Clay
25% Kaolin
50% Frit or Glass
Apparently there was also a soapy (talc) soft paste body. Maybe I could
simply replace the Whiting in the formulae above with talc.
Does anyone have any idea if I'm on the right track to duplicating 18th
century soft paste? Of course I'm not talking about bone china.
Peter Grieve
mailtoandrew@FSMAIL.NET on wed 30 jun 04
Hello Peter,
Your aim of recreating C18th porcelain sounds most interesting, though I
suspect it may prove to be quite frustrating.
From my understanding quite a number of the initial European attempts at
reproducing Chinese porcelain did use high proportions of frit or glass,
including some of the early UK manufacturers such as Bow, Chelsea,
Worcester and Derby. William Cookworthy is credited with the first to use
materials nearer to of the Chinese, clay and feldspar, and which are more
similar to most current porcelains.
A related material is Parian which was developed at Spode to mimic the
look of Classical Greek marble statues, the name being derived from the
Aegean Island of Paros. It is a mixture of kaolin, feldspar and glass; a
version still in production is Belleeck porcelain in Northern Ireland.
One of the very earliest European porcelains, known as Medici porcelain,
is described as .... sand and saltpetre were fritted and mixed with marine
salt, soda ash, plaster of Paris, and alum. This mixture was again fritted
and subsequently mixed with clay and plaster .... Reference: An
Introduction to the Technology of Pottery. Second Edition. Paul Rado.
Pergamon Press. 1988.
Amongst a number of porcelains Rado also describes magnesia porcelain
having been made using soapstone, that being talc or steatite, by
factories in Bristol and Worcester. A similar type is described from
Zurich and a sepiolte based porcelain from Madrid and Sevres.
Other recipes Ive seen in reference books include:
1. Lime marl 8, Frit 78, Calcspar 17 (that latter presumably is calcite.
And this adds up to more than 100!)
2. Kaolin 35, ball clay 15, quartz 20, frit 30
Of course these are relatively generic as the choice which kaolin, frit
etc is huge.
All this does illustrate that caution is needed with the meaning of
porcelain. With long use as a term for a range of bodies the only common
characteristics seeming to be the use of some clay and fired to
vitrification; and the definition of vitreous varies!
The description of True porcelain that has been used to differentiate from
what was described as false or artificial porcelain seems to have been
more a commercial term. Possibly originated by traders of Chinese ware
trying to protect business from European ware.
Even the term you used, soft paste, can have different interpretations,
including:
1. A body fluxed with glass or frit
2. A relatively description of the hardness of the fired body
3. Reference to the firing schedule used: soft being high biscuit and low
glost as opposed to hard being low biscuit and high glost.
My thoughts about recreating an C18th porcelain are:
1. Which one? It is highly likely that every factory had their own
formulation, which possibly varied over the years of production.
2. Raw materials used then are possibly not available now.
3. Working back from a modern analysis of an old porcelain can be a start
but the same end result can be achieved by any number of precursor
materials.
4. As you noted plasticity is likely to be low, and therefore casting is
probably a more suitable shaping method. And with low green strength great
care with handling would be needed.
5. Given the high glass content the pyroplastic deformation could well be
extensive; this is believed to have been a big problem at some of the
early factories.
If I may make a suggestions? Undertake as much research as possible
including ask all who may be interested before starting your own trials.
Given success the material could then accurately be described as a modern
interpretation.
I hope you will share your experiences with ClayArt.
Best of luck,
Andrew
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