Brooke Stoyer on thu 26 feb 98
I am an art teacher specializing in drawing and painting. Last
semester I tried an Indian Pottery project with my 7th and 8th
graders.
QUESTION: How does underglaze work? What temperature does it fire
at, and what is the end result supposed to look like?
When I fired the pottery, the underglaze was powdery and came off
easily. What could I do to remedy this?
Lili Krakowski on fri 27 feb 98
Not really happy with your using undergalze with kids. A lot of that
stuff is not exactly safe because a lot of colorants are toxic, and in an
underglaze they are in a very concentrated form. Underglaze essentially
is colorant that has been premixed and standardized so that you get the
same every time. I think it comes in liquid as well as powder form, but
even liquid is not great for kids UNLESS THE MANUFACTURER TELLS YOU IT IS.
Leaving that aside you are not telling us if you use the stuff on bisqued
ware or leatherhard or what. My own suggestion actually si to gt off
underglaze and use colored slips. Perfectly authentic for indian ware and
all around less problematic becaue undergalze can get quite tricly with
glaze fit.
On Thu, 26 Feb 1998, Brooke Stoyer wrote:
> ----------------------------Original message----------------------------
> I am an art teacher specializing in drawing and painting. Last
> semester I tried an Indian Pottery project with my 7th and 8th
> graders.
>
> QUESTION: How does underglaze work? What temperature does it fire
> at, and what is the end result supposed to look like?
>
> When I fired the pottery, the underglaze was powdery and came off
> easily. What could I do to remedy this?
>
Lili Krakowski
Donna J. Fisher on fri 27 feb 98
bstoyer wrote:
> QUESTION: How does underglaze work? What temperature does it fire
> at, and what is the end result supposed to look like?
>
> When I fired the pottery, the underglaze was powdery and came off
> easily. What could I do to remedy this?
Underglaze is a colorant used to decorate greenware. It can also be
applied to bisqueware and then covered with a glaze. Underglaze is
fired to about Cone 05 when used in design work but may be fired higher
(to about Cone 6) to achieve intensity and brightness though higher
firing may cause change or disintegration of color.
Two effects can be achieved with underglaze: If left unglazed (ie. no
coat of glaze applied over the underglaze), the colors will look
velvety. If a coat of transparent matte glaze is applied over the
bisque-fired underglazed piece, it will take on a satin, matte finish
when glaze fired. If covered
with a clear, transparent gloss glaze, the color will intensify and
appear more glossy. Underglaze can also be mixed like paint to create
other colors.
Glaze is made of materials which fuse together covering the piece in a
vitreous layer. The firing process causes glaze literally to melt and
spread over the piece. Underglaze, on the other hand, remains exactly
where it was placed; that's why it is used for design work.
Your underglazes came off powdery after firing most likely because the
pieces were under-fired. Try re-firing them higher.
---------------------------------------
DONNA J. FISHER
Community College of Allegheny County, South Campus
1750 Clairton Rd., West Mifflin, PA 15122-3097
(412) 469-6294 voice (412) 469-6370 fax
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