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slip or glaze?

updated sun 16 sep 01


David Hendley on sat 15 sep 01

Sandy was asking if it is possible to formulate a 'slip/glaze'.
I do this all the time, by making slip glazes that are glossy
like glazes but applied like slips.

There is no rigid line between 'slip' and 'glaze'. A slip can be
glossier and more fluid than a glaze.
After firing it can be impossible to tell if a coating was a 'slip'
or a 'glaze'; the distinction has more value when differentiating
how and when it was applied.
The same glaze formula (molecular formula) can be made into
a recipe that is used like a glaze or used like a slip.

Here's an example:

Ohata Iron Red Glaze (Cone 10)
Custer feldspar 42.35
flint 19.00
whiting 8.66
bone ash 8.66
talc 6.33
kaolin 5.50
red iron oxide 9.50

Ohata Iron Red Slip
Custer feldspar 25.00
Redart clay 32.00
bone ash 9.00
whiting 8.30
red iron oxide 7.20
talc 4.50
flint 13.00
soda ash 1.00

The unity formulae for these two recipes are identical:

CaO .60
MgO .17
K2O .14
Na2O .08
Fe2O3 .21
P2O5 .10
Al2O3 .32
SiO2 3.18

However, the recipes are quite different. The glaze recipe has
only 5.5% clay, but the slip recipe has 32% clay, making it
suitable for application to just-made clay surfaces.

An easy way to try using a slip-glaze is to buy (or make) some
low-fire white casting slip. The typical recipe for such slips
is 50% talc and 50% ball clay, plus a defloculant. At cone 10
this slip will make a white low silica matt glaze. Add oxides to
make colors; cobalt will produce purple because of the massive
amount of magnesium in the slip.

David Hendley
Maydelle, Texas

----- Original Message -----
From: "Sandra Talarico"
Sent: Friday, September 14, 2001 9:15 AM
Subject: Re: Kaleidoscope pottery

> Dear Made O Mud,
> I guess my question really was, is there such a thing
> as a slip/glaze? Something that would yield the kind of
> colorful glaze that I saw. I'm used to working with flat
> color slips and engobes. Colors that are flat blue, yellow,
> brown, or whatever. So, I was suprised to see these leaf
> patterns distinctly within a glaze.
> Sandy Talarico