Antoinette Badenhorst on thu 28 jul 05
Hi Guys, I'm sticking my head out here again. The porcelain recipe thing
triggered my interest again and I was wondering about combining bone china
(at powder stage) with porcelain mix. Of cause plasticity will be the main
thing for throwing again, but can there be any point in this and did anyone
try this before? I get the idea that there are some recipes for porcelain
that goes across the line to bone china. Is that true or not?
Antoinette Badenhorst
105 Westwood Circle
Saltillo MS, 38866
www.clayandcanvas.com
Dave Finkelnburg on thu 28 jul 05
Antoinette,
You ask a really interesting question. It would be fun to see what happens if you test it.
From my reading on bone china, the one thing that comes through very clearly is the bone china body has a very narrow firing range, much narrower than that of porcelains. So, you first need to know what that temperature range is, and then have a kiln and firing program that duplicate it consistently. How that applies to a mix of the two, I'm don't know. I think all you could do would be to test it.
Good potting!
Dave Finkelnburg
Antoinette Badenhorst wrote:
The porcelain recipe thing triggered my interest again and I was wondering about combining bone china (at powder stage) with porcelain mix.
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pinacoid3000@LYCOS.COM on thu 28 jul 05
Hello Antoinette,
Precise definitions of ceramics bodies can be a little difficult, however
for bone china there are two:
The British Standard defines that the fired ware must contain 35% by mass
of tricalcium phosphate. Whilst this is recognised in most countries the
US allows a reduced level, and is defined by the unfired body, where 25%
bone ash is needed. Thats not to say bone ash can not be used in bodies at
lower additions just that it would not be bone china
Whilst the classic bone china recipe of 50% ash, 25% china clay and 25%
flux does not give the most plastic of bodies the appropriate raw material
selection can help:
1. Ash. Natural bone ash imparts a little plasticity, although not much,
whilst synthetic grades add nothing
2. China clay. Use the most plastic. Did you find the information on Super
Standard Porcelain I noted in a previous post?
3. Flux. China stone results in a more plastic body than standard feldspars
If that still isnt sufficient try a little, perhaps 1%, of a clean
bentonite. This really does need to be kept to a minimum as it will give
high shrinkages, and hence more likely to crack, and cause reduced fired
whiteness
Hope that helps,
Andy
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