[Clayart] no labor porcelain

Robert Harris robertgharris at gmail.com
Tue Dec 29 22:25:13 EST 2015

Just as an addendum to what you say Ric. As far as I know all U.S. Kaolins
(or at least the commercially exploited ones) are secondary clays.
Whereas several of the European Kaolins (e.g. those from Corwall, and
France, used to make Grolleg and Limoges porcelains respectively), are
primary clays and therefore do not have the extra titanium that prevents
translucency in many domestic porcelains.

On Tue, Dec 29, 2015 at 5:32 PM, Ric Swenson via Clayart <
clayart at lists.clayartworld.com> wrote:

> just a few points of interest.....and hoping not to labor a point...
> from my living in China for the past ten years... and as a potter and
> teacher since 1967...
> A Primary clay...one broken down by many  thousands of years by natural
> erosion factors and not moved to secondary locations which would pick up
> other minerals such as iron, etc.... is rather pure.
> In China at a mountain of such clay in ' Gao Ling' village  (we pronounce
> it 'kaolin' in English) was found in about 1004 AD and used by potters
> since then to make ceramic wares.
> Potters in nearby Chang Nan ( now called JingDeZhen, because the Emperor
> changed its name to label it after his reign because he appreciated  the
> blue and white wares made there.) made ceramic wares of this clay....and it
> became popular world wide.
> Portugal's shipping traders first brought wares from China  to Europe and
> people wondered at the pure white clay...as white as the white sea shell
> PORCELANA...hence the name we use now..
> Folks asked where did this ware come from?...and they answered  "CHANG
> NAN"  which we now call CHINA.
> Or as I simply have said to my many students over the years...there are
> basically just three types of clay:
>  Terra Cotta ( Italian for  common"earth clay") which is found in the
> earth's crust in many locations ...it is contaminated with iron and other
> minerals.. it is classified as a  SECONDARY clay because it has been
> carried  by water...rivers...rain... from where the granite rock first was
> broken down by nature and turned to the microscopic rather long and  flat
> plates of clay...It fires at low temperatures ( 800 C. or lower)  Some call
> it brick clay. It can be reddish/brown or gray (grey) after firing. Clay
> made with TALC also fires at low temps and is commonly used to make white
> cast wares you see in hobby shops...it is suitable for decorative use but
> not as durable as higher fired wares.
> Stoneware is the second. Usually blended with some  feldpathic materials
> and fires in a range of cone 6-10..about 1000 C.  Fired colors can range
> from light grey to nearly black depending on  its mineral makeup.
> Porcelain is always fired at high temperatures .  Cone 10-14 or about 1300
> C. It is pure white...(or as we refer to it in Jingdezhen....As white as
> Jade, thin as paper, bright as a mirror, and sounds as a bell.)  It usually
> is combined with feldspar now-a-days for the fusing properties it adds. It
> 's difficult to throw larger pieces... and thus a lot of trimming is needed.
> ric
> >
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