Stephani Stephenson on wed 15 may 02
William Wrote:
I wanna make a white underglaze that I'll be firing to c04. I've =
searched through the clayart archives and elsewhere and found recipes =
that call for stains in what seems to be unusually high amounts.
The Ceramic Supply catalog has a recipe calling for 2 parts frit, one =
part stain. The Highwater Clay recipe is a 30-30-30 mix of frit, EPK, =
and stain. And a third, found in the Clayart archive and supposedly from
=
Mason, calls for 20 parts F4, 10 EPK, 5 Ball, 10 frit, and 40 stain. =
Converting these recipes into percentage terms, the first two call for =
50% stain while the third calls for almost 99% stain! =20
Presuming that this was yet another glaze mystery I didn't understand I
=
called Mason where I was told that 10% should be sufficient. That's a =
really BIG difference. So before I plunge ahead, spending lots of money
=
on stain, I'd like to hear some opinions from the list. Is it really =
necessary to have these high amounts of stain to get color density? And
=
just what other alternatives do I have to mix my own?
Thanks,
William
William, As I read it you are describing a couple of different uses for
stains.
First, it sounds like you want a white base underglaze that you can
tint with different colors of stains.
The percentage of stain you use will vary of course, depending on the
intensity of the color you want (pastels v. saturated hue)
generally, 2% - 10% will do the job, though some weaker stains, such as
certain yellows require 10%-15%.
Some stains are more refractory than others so the larger proportions
may affect the 'dryness' (appearance) of your fired underglaze.
So if you are tinting a white base, 10% usually is sufficient. But ,
again the percentage will vary.
The Ceramic Supply recipe you describe is useful when you want to use
the stain alone as a tinting, or color application on the clay.
The 2P frit :1 P stain or even 1:1 ratio of frit to stain is not
unusual for this kind of application, i.e. where you want the look of
the stain itself, rather than as a tinting agent in an opaque
underglaze. These can be thinned down with water (also brushing medium
or suspension agent,) so they actually go a long way, even though it
sounds like you are using a much higher percentage of stain.
Lets start with the stain itself. You could just thin a mason stain with
water and paint or spray or daub it on. , i.e. 100 % stain.
Only problem with this at cone 04 is that some of the stains will not
fire on, but will still rub or wash off after the firing, when used
alone.
Unlike iron oxide , which WILL flux and melt and bond with the clay
body at that temp, many other stains need some added flux to ensure they
'stick ', or fuse to the clay.
When a glaze is applied over them, most stains or stain/frit combos
will flux sufficiently. However, stains used alone or with frit will
not provide much opacity . (though , some frits DO have an opacifier,
and in fact, some Mason stains do too, so it does depend on which frit
you use and which stains...)
In my mind a white underglaze will have some clay (usually EPK), which
will as a suspension agent, and help the underglaze fit the shrinkage
of the clay body. With its silica and alumina, EPK will also provide
some surface durability, and some opacity. An underglaze may also have
an additional opacifier like zircopax. and some type of frit to aid in
fluxing, and other ingredients.
I have found some useful engobes as base recipes in Chappell's book.
Also another VERY uselful underglaze base is dry white casting slip (I
have used cone 06 and cone 6)
Add water, makes a lovely white slip/underglaze ... add stains.
Of course, as you experiment with making an underglaze, you may find,
that the hardest part is finding an underglaze formula that 1: fits
your clay body 2: provides a durable surface by itself (no flaking, not
to soft), or a good interaction with overglazes( right amount of
opacity, melt, etc.) 3: provides the visual appearance you desire 4)
provides the application qualities you desire (flows on with painting,
etc)
so again...test, test test. measure, measure, measure.take notes, take
notes take notes.
Good luck!
Stephani Stephenson
steph@alchemiestudio.com
Carlsbad CA
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