Craig Dunn Clark on thu 6 nov 03
clay body cone6,10, 12 etc.
I have been under the impression that a clay body that is formulated to
reach it's optimum point of vitrification at cone 6 is just as strong as one
that is formulated to vitrify at cone 10 or higher. Have I misunderstood
Craig Dunn Clark
619 East 11 1/2 st
Houston, Texas 77008
----- Original Message -----
From: "John Hesselberth"
Sent: Thursday, November 06, 2003 6:26 PM
Subject: Re: cone 6 as ovenware?
> On Thursday, November 6, 2003, at 03:32 PM, John Rodgers wrote:
> > But vitrified claybodies should not have this problem. Water is not
> > entrained. Vitrification can be accomplished at cone 6, but at cones
> > like 10,11, and 12, it's the best, and the ware is a lot stronger to
> > resist breakage of any kind.
> I could easily make the case that cone 6 is preferred over cone 10-12
> for ovenware. First it can be adequately vitrified with no problem--not
> by using a cone 10 body at cone 6, but by using a well formulated cone
> 6 body. Second, cone 6 does not normally have a cristobalite
> problem--cone 10 bodies can easily have this problem if they contain
> excess silica and that is bad news for oven ware. The cristoballite
> phase conversion occurs at 226 deg C (439 deg F)--within the range of
> normal oven temperatures. This results in a rapid 3% change in volume.
> That can easily crack a casserole dish. Of course, properly formulated,
> cone 10 bodies should be OK also, but it is a lot easier for a potter
> to tell if a body is properly vitrified than if it (at cone 10-12) has
> a cristobalite problem.
> So my answer to your question is that cone 6 stoneware is fine for
> ovenware if you make sure the glaze is durable and fits well, and the
> body is well vitrified (below 3% water absorption). It may well be
> preferred over cone 10-12.
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John Hesselberth on fri 7 nov 03
clay body cone6,10, 12 etc.
On Thursday, November 6, 2003, at 08:47 PM, Craig Dunn Clark wrote:
> I have been under the impression that a clay body that is
> formulated to
> reach it's optimum point of vitrification at cone 6 is just as strong
> as one
> that is formulated to vitrify at cone 10 or higher. Have I
I suspect this is similar to arguing about whether Macs or Windows
machines are faster. Properly vitrified, both types of bodies are
plenty strong for functional work. I've never seen a well-designed test
trying to prove that one or the other was 'stronger' and I'm not even
sure how I would design one if I wanted to. There are so many other
variables involved which could have at least minor effects on a body's
physical properties. Deciding on where to set those variables and
holding them constant would provide meat for several graduate level
theses and even then there would still be plenty of room for ongoing