Russel Fouts on fri 4 sep 98
In ANOTHER article by "Pete Pee" (does he get the award for most quoted?) he
mentions putting Magnesium Carbonate (Epsom Salts) in a glaze to thicken it.
I tested it with some sig and although it thickens it only very slightly
(probably all that water) it does make the sig go on thicker. I get thicker
coats with fewer dips and it seems to polish better. I haven't tested it on
any "real" pieces yet but I think it will make it adhere better and be more
This is my reasoning. The sodium silicate I use to make the sig (and which
stays in the finished sig) causes the clay paricles to form a "stack of
cards" structure on the surface of the pot when it's dipped. This quickly
seals the pot from absorbing more water and more sig and makes it take a
long time to dry. It also keeps the structure closed so you might get even
less sig the next time you dip.
The Epsom Salts reverses this and makes the clay particles form a "house of
cards" structure on the surface of the pot which is more open allowing more
water to be absorbed (thus more sig to get attached) and allowing the pot to
dry quicker. It also keeps the structure open when it drys so you can get a
thicker coat next time too.
With out the Epsom Salts, it takes 4 coats to cover. With the Epson Salts,
it takes two. This is a great savings in time since I usually have to let
the pots dry a day between dips (mostly due to the humid Belgian climate).
Does anybody else have any thoughts on this?
Mes Potes & Mes Pots
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Vince Pitelka on mon 14 sep 98
>mentions putting Magnesium Carbonate (Epsom Salts) in a glaze to thicken it.
>I tested it with some sig and although it thickens it only very slightly
>(probably all that water) it does make the sig go on thicker. I get thicker
>coats with fewer dips and it seems to polish better. I haven't tested it on
>any "real" pieces yet but I think it will make it adhere better and be more
Epsom salts may work great for thickening a glaze, but it goes completely
against the whole theory of terra sig to use epsom salts to thicken it so
that you need less coats. By using epsom salts (a flocculant) you are
neutralizing the deflocculant which helps make the sig do what it does. The
deflocculant (soda ash, sodium silicate, etc.) makes all those
ultra-microscopic particles stay in suspension, so that you get a reasonable
amount of coverage even with a very thin coat. You do not want it to go on
thick. You NEED to put it on in multiple thin coats. True terra sig never
responds well to thick--single-coat applications. I would guess that you
will have some serious problems with peeling and flaking when the pots dry
or during/after firing. Please let me know how your experiments turn out.
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166