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Old 27-05-2004, 09:11 PM
Lynn Boyd
Posts: n/a
Default [IBC] Ceramic Pots 1


Thanks for this effort - it is helpful as text to grasp
the picture for newcomers curious and inexperienced with the
"pot" appreciation part of bonsai/penjing.

I'm glad to hear you stay at it. I still spend a lot of time
with potter friends and don't miss a firing, but as for the
clay throwing my hands took me out of that except for the
occasional small raku. It is great that we have some very
fine potters in IBC.

With regards to bodies:

Stoneware [traditional]
Vitrification is between 3 to 5 %[or what ever is on the
packaging of the clay powder.]

If exceeded,past the %[seen above],the body will
have too much glass.It will then be more susceptible to
Thermal shock[the stress created within a ceramic object
by temperature change.Thermal shock is responsible
for the occurrence of cracks and is an OVERALL term,
pg.320 The Potter's Dictionary-Hamer 3rd edition.]

So freeze/thaw as experienced in winter or sun on a cold
pot or possible expansion of water in soil and so on
[which is what I meant and hoped would be understood
because there is a great deal of Japanese information

with winter care.]Could after slow time damage a pot.
Especially since most pots already have fine cracks present
in the body after firing.

Raku bodies resist this damage because of the particles
within the body blocking the crack from physically passing.

I don't know,and wasn't talking about the absorption of

into the stoneware body and then freezing.

On Porcelain.

In porcelain the body is homogenous;it does not contain
variously-sized particles of sand,grog etc.
[ The Potter's Dictionary -Hamer pg.312 ]

Stoneware isn't homogenous,but this article deals more with
glazes and but I think the above is enough to explain the

in response between the two clay types.

I have no way of know how porcelain pots handle cold.

All that said.

Today's clay bodies are often designed and books now
carry these categories.

Soft Stoneware
Hard stoneware
Stoneware type
Hard Porcelain
Soft Porcelain
Low fired Vitreous
Low fired Translucent
Ultra low fired Vitreous
Ultra Low fired Translucent
Bone China
Boron Phosphate Bone China
Low fired Bone China
Ultra Low fired Bone China
High fired Earthenware
Low fired Earthenware
add on Vitreous/translucent to
the above as well as Ultra low.

and so it goes.
Temperature range is 750 to 1400 deg.c
and so on.

As to finishes on the body.
Anything goes.

You can have,
Stain coloured bodies,dark or light.
Slip coloured bodies
Smoke/reduction/carbon coloured bodies
Glazed coatings
Enamel coatings
Hard resin coatings
and so on.

I am sorry,I did want to throw all of this at the group.

Glazed on the inside problems-
I think that breathe bit comes from high fired
but still say 8% porous earthenware ,with probably heavier
[Not everyone is too bothered by the salts deposited
on the outside of the pot.]

This is probably still popular with those using more
traditional soils.[The Yi Xing pots are supposed to
be the best here for these soil types.]

I have a few plants in porcelain pots that are exterior
glazed,but I use freely draining mixes.I believe the
plants would have died in heavier [perhaps clay based]
So I would say the comment is true if using heavy soils,
but not so for freely draining soils.

If your still reading,I will let the newcomers know that I
have been in pottery for about 25 years.I dig,clean and
process my own clay bodies.I specialise in Low fired
vitreous bodies [ 980 deg.c and lower.],Egyptian Paste
[980 deg.c orton 08 small cone ] making my own glazes
and enamels from oxides/carbonates and ground glass
cullet.I have a ball mill.

I do not sell my objects,just give them away as gifts.
So I do not make a living through pottery and am not
a professional,just a serious hobby.
West Indies/Caribbean.

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