[Clayart] wrong clay, wrong glaze

[Vince Pitelka]

I like Paul's criteria that porcelain be iron-free, or as iron-free as is possible.  My criteria of pure white is not really appropriate, because much true porcelain is slightly off-white.  Zero porosity is a pipe-dream.  It is possible, but there is plenty of porcelain that does contain a small fraction of porosity, and of course there is plenty of wonderful historic porcelain that is not translucent, so that isn't really an appropriate criteria, especially in this day and age.  I would like to propose this definition: "Porcelain is the fired product of white or off-white-firing claybodies that are very low-iron, fired to maturity at midrange or above such that the fired product is extremely low-porosity."  

How's that?
- Vince

Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka at dtccom.net  
https://sites.tntech.edu/wpitelka/
 



-----Original Message-----
From: Clayart [mailto:clayart-bounces at lists.clayartworld.com] On Behalf Of Vince Pitelka
Sent: Sunday, November 6, 2016 8:14 PM
To: 'Clayart international pottery discussion forum' <clayart at lists.clayartworld.com>
Subject: Re: [Clayart] wrong clay, wrong glaze

I am pretty sure we already have come to some contemporary consensus of what constitutes porcelain.  It seems that the definition has been expanded from the traditional one to include vitrified pure white cone-6 bodies, and if we accept that (as I am sure some traditionalists will not!), I think we can agree that midrange and high-fire pure white claybodies that are grit-free and have extremely low porosity when fired to maturity can be called porcelain.  But as was pointed out in a previous post, no claybody advertised as "porcelain" actually becomes porcelain until it is fired to maturity with extremely low porosity.  If it is underfired, it is not porcelain.  A "porcelain" claybody is called that only because it is capable of becoming porcelain when fired properly.  
- Vince

Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka at dtccom.net  
https://sites.tntech.edu/wpitelka/
 


-----Original Message-----
From: Clayart [mailto:clayart-bounces at lists.clayartworld.com] On Behalf Of Paul Gerhold
Sent: Sunday, November 6, 2016 3:04 PM
To: Clayart international pottery discussion forum <clayart at lists.clayartworld.com>
Subject: Re: [Clayart] wrong clay, wrong glaze

Yeah, but Mel try to get the people on this list   to agree on a definition of porcelain. Been through that before and you get hammered because probably half the people are using a white clay that their  vendors pretend is porcelain and they get very defensive  because they think being technical is the antithesis of being an artist.

Heck I bet you can't even get a consensus on what constitutes vitrification.

Paul 

Sent from my iPad

> On Nov 6, 2016, at 8:45 AM, mel jacobson <melpots2 at visi.com> wrote:
> 
> as to kathy's stories and john's report.
> 
> i was at the excelsior sidewalk fair near my home.
> walked into a booth with a sign `porcelain`.  i picked up a cup and stuck my tongue on the bottom.  it stuck like velcro.  i asked the young woman if this was porcelain....?
> `yes, like the sign says`.  i said.  `this is not porcelain`.
> of course she was using continental clay white stoneware, (several empty boxes to carry pots, or something with a B name) fired to cone 6 with some sort of white glaze with flowers in color.  she did not have a clue.  i just walked away.
> no use going any further with the conversation.
> 
> and, i guess that is my bottom line. none of us know what is in commercial clay bodies.  we have talked about this for nearly twenty years.  does it vitrify at cone 6??? probably not.  is it a broad range clay????they say so...but how can it be.  cone six clay should be totally vitrified at cone 6.
> 
> it becomes a fact that none of us are any better off because  the gal on the street is selling that crap and the society at large has no knowledge of what they are getting.  she becomes a standard...can't help it.
> 
> if the thousands of hours of work ron and john have done to help us understand gets washed into the sewer with bad clay...we have all lost.  we have to get folks to match the glaze and the clay body, and that may take pressure on the vendors to make sure that happens...if they sell it to us, it should vitrify at cone 6.  electric.
> 
> i have cups in my cupboard that i made in 1966. they are the same as the day they came from the kiln.  everything we eat from is from my kiln, or close friends kilns. every day, for  fifty years. it is solid and vitrified.  my planters do not leak.
> 
> i cannot ever thank ron and john enough for their service to the clay community. ron even checked my rhodes 32 and realized i had added silica and titanium to my glaze to make  it tighter. i am concerned.  and, i have to do it right if we are going to splash clayart with new ideas.
> 
> we often thrash around here on clayart...lots of opinions and ideas, but it always seems to come back to the original idea...`understand your materials, know what you are doing, and do it with skill and concern.` LISTEN TO EXPERTS.
> the big problem is so many that teach do not have a clue.
> those that do, stand out like beacons.
> mel
> 
>