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burning off unwanted glaze

updated sun 2 jan 11


jan on sat 1 jan 11

i am relatively new to this game. a sycophant of form. a neophyte when it=
to glazing...
i glazed a carved form and muddied/filled up the relief.=3D20
commercial moroccan sand glaze to cone 5 on a #80 laguna cone 4/6 clay.=3D2=

i am wondering if i fire the whole mess at a higher temp can i burn off t=
he glaze=3D20
without harming the clay?
thank you for all the advice i regularly receive from you all. not having=
ceramics the list is a treasure trove of mentors.
cu in tampa. jan

Snail Scott on sat 1 jan 11

On Jan 1, 2011, at 8:44 AM, jan wrote:
> i glazed a carved form and muddied/filled up the relief...
> i am wondering if i fire the whole mess at a higher temp can i burn =3D
off the glaze=3D20
> without harming the clay?

Not really. It will get runnier, and might thin out a bit,=3D20
but the carving will be the last part to thin out, and it=3D20
may stay filled up even if all the rest runs off. Also, if=3D20
you fire much hotter than the optimum vitrification=3D20
point for your clay, it may warp and/or develop glaze=3D20
fit issues. You will never be able to remove any glaze=3D20
entirely, not even with sandblasting.

I'd chalk it up to a learning experience. Hard to accept=3D20
if you put a lot of work into it, but for this piece, I'm=3D20
afraid you've got what you've got.

Two lessons I'd take away from this:

1. Some glazes are very responsive to texture, and=3D20
can enhance the look of relief carving, either because=3D20
they are somewhat transparent or because they change=3D20
colors where thin. Seek out such glazes! If you aren't sure=3D20
which glazes will serve, buy from a local supplier where=3D20
you can go and inspect fired samples of the glaze you=3D20
have in mind. If you buy glazes mail-order, look for any=3D20
symbols or notes that indicate transparency or 'breaking'=3D20
(that's the term for changing color where thin). Feel free=3D20
to call or e-mail, too, and ask the manufacturer. Most of=3D20
them are small companies, and they will be happy to=3D20
advise you if you explain what you want.

2 ALWAYS TEST! Even if you have a glaze that is=3D20
likely to do well, you need to test it on your own clay,=3D20
using your own application technique, on your own=3D20
typical textures, and fired in your own typical manner.
All these factors affect the look of a glaze, sometimes=3D20
very strongly. Don't use your precious time-consuming=3D20
projects as tests. Instead, make up small sample scraps=3D20
using similar surface textures. Make the sample pieces=3D20
big enough that you can get a good look at the effect=3D20
after firing. (Imagine having a couch upholstered in a=3D20
fabric that you only saw a 3" swatch of!)=3D20

Here's some good ways to do test tiles. (We call them=3D20
'tiles' regardless of shape.) A: Roll out a slab and cut=3D20
it into 2" or 3" wide strips, 5 inches long. Texture the=3D20
surface and bend one end into a 'foot' so it can stand=3D20
up. (Tiles that lie flat only show you what the glaze will=3D20
look like on a flat want a vertical surface=3D20
that emulates your actual work.) B: Throw a short wide=3D20
cylinder about 4" high, with no floor. Slice it into 2" wide=3D20
vertical pieces, and texture as appropriate. C: Throw=3D20
lots of narrow cylinders and texture as appropriate.=3D20
This is more work than the other methods, but it is=3D20
good practice, and if any of the tests look good, you=3D20
can call them 'cups' and sell them! Whatever method=3D20
of test-tile-making you choose, label each one with=3D20
a numbering system scratched with a tool or drawn=3D20
in iron oxide, and list each test in a notebook so you=3D20
can keep track of your results.=3D20

There's a lot you can learn doing tests, without risking=3D20
all the time and emotional commitment of an elaborate=3D20
carved project. Once you get some promising test=3D20
results, then try it out on a real project. It will still look=3D20
a bit different from your test; it always will, but you will=3D20
get more consistent with practice, and your tests will=3D20
be more and more useful.


William & Susan Schran User on sat 1 jan 11

On 1/1/11 9:44 AM, "jan" wrote:

> i glazed a carved form and muddied/filled up the relief.
> commercial moroccan sand glaze to cone 5 on a #80 laguna cone 4/6 clay.
> i am wondering if i fire the whole mess at a higher temp can i burn off t=
> glaze without harming the clay?

The clay and glaze may be capable of being fired to a higher temperature,
but how much higher, I don't know - perhaps cone 7 or 8.

But firing one piece to a higher temperature is not necessary. Try just
re-firing it in your next Cone 5/6 firing. The glaze will melt more and may
produce desired results.


William "Bill" Schran