Ron,

Roughening of the surface, whether by stuccoing, indenting, brushing or any 
other method, increases the amount of surface area available to serve as a 
"heat exchanger" ... additionally, a roughened surface causes turbulent 
currents (in the heated air streaming by the exterior) on the surface, which 
do not necessarily increase the coefficient of heat transfer (efficiency) of 
the surface, but does tend to "regulate" it (slows down abrupt changes in 
temperature) within a more moderate amd predictable range (that is, the pot 
is not so sensistive to its alingment over the heat source/fire ... 
consequeently, doing away with hot and cold spots ... that, incidentally 
gives another decided advantage, making the pot less susceptible to breakage 
from the shocks of localized hot & cold spots ... "chunky" temper of the 
right kind and size also conferring these advantages).

Consequently, as a general rule (across all cultures that I am familiar with 
in Northern America), the cooking pots almost always have roughened (or at 
least non-smoothed, non-polished) exterior surfaces.

Bob Skiles


----- Original Message ----- 
From: "Ron May" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, July 03, 2009 4:12 PM
Subject: Re: Temper


> In addition to mica to control heat, some potters "stuccoed" the exterior
> of pots with clay to control heat. I have examined stuccoed pottery, but
> really  do not understand how this helps in heating. Any ideas?
>
> Ron May
> Legacy 106, Inc.
>
>
> In a message dated 7/3/2009 3:14:07 A.M. Pacific Daylight Time,
> [log in to unmask] writes:
>
> Mica  could enter the pot as temper (with quartz sand) as micaceous
> sandstones  are not uncommon at least in Europe.
>
> I came across an interesting  example recently from a kiln in Swansea, S
> Wales. it produced pots which  appear t be late C15/early c16 in date
> paralleling similar vessels from  the Cotswolds (Minety area) suggesting
> a source for the potter. The  Cotswold pots are tempered with oolitic
> limestone but the Swansea pots  appear to have been tempered with an
> oolitic sand probably from a beach  along the nearby Gower peninsula. The
> pots re unknown from consumer  deposits so it looks as if the kiln was
> short-lived- possibly not much pot  being used in this period which seems
> to be dominated by English and  Continental  imports.
>
> paul
>
>
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