[Clayart] commercial clay/VITREOUS

David Woof woofpots at hotmail.com
Thu Apr 5 23:32:25 EDT 2018

Just a reminder from a word "nit picker"... "Fully Vitrified" would "**Most Likely**" (lawyer PMA) pluck, slump, or depending on the form, sag and or sag and crack open in a slumped ragged tearing of the wall.

The clay bodies I've developed and worked with were kept between 1.7 and 0.5 absorption depending on materials used in the body. Some cone 6 stoneware bodies (especially red) began to seriously pluck at 0.5, where as porcelain at 0.5 is usually a good tight place to be.

It would try my patience to the "red zone" so I have never bothered with oil lamps for the reasons David H just mentioned. He has it dialed in! But still, Micro aggregate/filler occlusions due to internal separations and/or failure to create a tight glassy matrix in the body, that wouldn't cause a problem with water, can bring folks back with an oil leaker.  Saw enough of other potter folk's oil leakers back in the "Hippy Potter daze."

David Woof


From: Clayart <clayart-bounces at lists.clayartworld.com> on behalf of Snail Scott <claywork at flying-snail.com>
Sent: Monday, April 2, 2018 9:16 AM
To: Clayart international pottery discussion forum
Subject: Re: [Clayart] commercial clay/VITREOUS

> On Mar 30, 2018, at 9:51 PM, David Hendley <farmpots at eastex.net> wrote:
>  'semi-vitreous' is an OK description to me…

I’m fine with it, too. I’d visualize something tighter than most earthenware, but not impervious to moisture penetration. I’d see that description, and if it seemed like what I wanted, then I’d look to the numbers for more detail. ‘Fully vitrified’ isn’t always a requirement for every purpose.

I also perceive that most manufacturers give their data at a standardized cone - ^5 at Laguna, for instance - so if they are selling a body that optimizes at some other cone, it can look wrong. For example, a perfectly nice ^8 body might have to be described as ‘semi-vitreous’ at ^6.

The hazard is that when novices see something advertised at a particular cone, they believe that it all fits together like Lego, and that all clays and glazes fit one another perfectly for every purpose if it’s got the same number on it. That will always be the case when a complex craft is approached without solid understanding, and it will be. (Approached, that is - by anyone who wants to.) Should manufacturers sell only ‘Lego-like’ perfectly compatible products aimed at only one optimized function? Or should they sell anything that seems useful and sufficiently in demand to find a market niche, leaving it to the user to determine suitability for purpose?  Right now, most are taking a middle way, in which most materials are mostly compatible for a few popular purposes, but still offering a few outlier items requiring better knowledge. Nobody’s going to be perfectly happy with any of these three options, but I can live with this compromise, myself.

It’s easy to say that manufactured products are for amateurs and ought to be made foolproof, and that pros ought to make it for themselves, but this would come at the expense of variety and potential for those amateurs, and dictate appropriate working methods for pros who can darn well make their own choices for manufactured products or homemade.

Snail Scott
claywork at flying-snail.com

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