[Clayart] Clayart Digest, Vol 50, Issue 43

[Robert Harris]

I clearly remember back in the 80s 90s (and for all I know, now), they used
to sell “frost-proof” terra-cotta plant pots in the UK. The cheap ones used
to crack regularly when it froze ... probably a combination of water
freezing in the clay, as well as some pressure from the frozen water inside
the pot.

I’m not sure if they were an underfired red stoneware, or a terracotta with
some fireclay added that was fired hotter than normal, but they certainly
worked. They were also quite a bit more expensive, but certainly not so bad
that they didn’t end up taking over the market.

There is quite a fun little video out out by one of the makers of very
fancy terracotta plant pots in the UK. At the beginning of the video there
is a little bit about how they blend their clay, although it’s rather less
than specific!

https://youtu.be/9ALR6QV0kkw


R

On Fri, Jan 31, 2020 at 9:02 PM <vpitelka at dtccom.net> wrote:

> Hi Alice -
> It can't just be an open claybody.  According to Val Cushing, it must be a
> claybody with enough porosity that also has enough mechanical strength to
> withstand the pressure of the expanding freezing water.  That's why an
> underfired highfire body works well.  Fired earthenware is an open
> claybody, but it has little mechanical strength and will disintegrate in a
> hard freeze.
> - Vince
>
> Vince Pitelka
> Professor Emeritus of Art/Ceramics
> Appalachian Center for Craft
> School of Art, Craft & Design
> Tennessee Tech University
> Now Residing Chapel Hill, NC
> vpitelka at dtccom.net
> www.vincepitelka.com
>
> -----Original Message-----
> From: Clayart <clayart-bounces at lists.clayartworld.com> On Behalf Of Alice
> DeLisle
> Sent: Friday, January 31, 2020 11:34 AM
> To: via Clayart <clayart at lists.clayartworld.com>
> Subject: Re: [Clayart] Clayart Digest, Vol 50, Issue 43
>
> Ric,
>
> Val Cushing wrote about this in Cushing’s Handbook. Most potters assume
> that the best clay body for outdoor work is the one with the lowest
> absorption. According to Val’s article (and the ceramic engineers at
> Alfred) the reason that outdoor work breaks is that any absorbed water
> expands and contracts with freezing and thawing. Most clays absorb some
> water. An open clay body allows space for the water to expand and contract
> and is thus actually better for outdoor work than a closed clay body. The
> article includes an absorption test for outdoor work. The Handbook is
> available from the Pharmacy (book store) at Alfred University. I could send
> a copy of the short article if there is interest.
>
> Peter King wrote a related article entitled something like “Another Cup of
> Grog, Please”. A bit tongue in cheek!
>
> Alice
>
> Alice DeLisle
>
> wanderland at att.net
> https://www.facebook.com/IslandTexturesAliceDeLisle/
> https://www.flickr.com/photos/alice_delisle/sets/
>
> "Not all those who wander are lost…" – J.R.R.Tolkien
>
>
>
> > On Jan 31, 2020, at 4:29 AM, clayart-request at lists.clayartworld.com
> wrote:
> >
> > Date: Fri, 31 Jan 2020 00:31:40 +0000
> > From: Ric Swenson <ricswenson0823 at hotmail.com <mailto:
> ricswenson0823 at hotmail.com>>
> > To: Clayart international pottery discussion forum
> >       <clayart at lists.clayartworld.com <mailto:
> clayart at lists.clayartworld.com>>
> > Subject: Re: [Clayart] Best clay for outdoor sculpture
> > Message-ID:
> >       <
> HK0PR03MB3956E18D2824624EB0CA542EC3070 at HK0PR03MB3956.apcprd03.prod.outlook.com
> <mailto:
> HK0PR03MB3956E18D2824624EB0CA542EC3070 at HK0PR03MB3956.apcprd03.prod.outlook.com
> >>
> >
> > Content-Type: text/plain; charset="windows-1252"
> >
> > IMHO....A clay body that is vitrified (glass-like) to the highest
> temperture possible without deforming or bloating will last the longest
> outdoors. Freezing and thawing in a body that is not vitrified well will
> cause it to deteriorate over time.
> >
> > A coating of vitrified glaze will allow an outdoor sculpture to last
> much longer.  Common brick clay (Terracotta) that is fired too low will
> deteriorate over time...by spalling, flaking or erosion of the surface.
> >
> > The addition of grog to a sculpture body helps with drying without
> cracking but as long as the body is fired to high enough temp. it should be
> fine. A fired body with less than 1 % water absorbsion would be desirable.
> >
> > Other thoughts folks?
> >
> > Regards,
> >
> > Ric
> >
> > ________________________________
> > From: Clayart <clayart-bounces at lists.clayartworld.com <mailto:
> clayart-bounces at lists.clayartworld.com>> on behalf of Scary Potter <
> scary.potter at yahoo.com <mailto:scary.potter at yahoo.com>>
> > Sent: Friday, January 31, 2020 1:54 AM
> > To: clayart at lists.clayartworld.com <mailto:
> clayart at lists.clayartworld.com> <clayart at lists.clayartworld.com <mailto:
> clayart at lists.clayartworld.com>>
> > Subject: [Clayart] Best clay for outdoor sculpture
> >
> > Looking for suggestions from some of you fabulous experts - best Clay
> for cone 5-6 garden art?
> > What attributes should a clay body have for surviving outdoors?  More
> ?open?, more grog, less something? Do you have a favorite recipe or
> commercially available body you love?
> > I?ve only made small things with smooth clay but want to venture into
> larger garden sculptures this spring.
> > I normally fire to cone 5 or 6.
> >
> > S.Cary -
> > Make something beautiful every day.
> > Scarypotter.com <http://scarypotter.com/>
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