glazing thin porcelain

updated mon 31 mar 97

Joan Warren on wed 12 mar 97

Hi there pocelain people,
I'm having a terrible time getting my glaze to absorb on the edges of my
porcelain bowls. I'm trying to achieve a fragile shell-like form, and the
thinner I go , the less glaze they absorb. I,ve tried bisquing lower (010)which
helps, but they now break in my hands when glazing. I've tried using gum and
less water (like yogurt), and wheel brushing the glaze , but that has it's
limitations, and shows brush-marks. Spraying is no better. Any suggestions?
Thanks in advance.
Joan Warren

katepwa@raven.bc.ca
sent via UUCP from: Raven Net, Salt Spring Island, BC, Canada

Karen Gringhuis on thu 13 mar 97

Joan - when dbl. dipping porcelain (not thin) I dry w/ a heat gun.
What if you heated up the rims before dipping? Karen Gringhuis

Clay on thu 13 mar 97

Any commercial glaze-maker here?
I've been using Spectrum/Duncan dipping glaze for earthernware glazes. I
used to have the exact problem with my plate. & the chemist of those company
talking about adding their secret ingredients in it (instead of water. What
it does is delay the drying time (I found) it run much slower, but it even
out the whole body that you glaze.

Actually anybody have a clue what they actually put into it?

Gum, I did it before paint it on the edge first & spray. It takes forever to
finished.
>Hi there pocelain people,
>I'm having a terrible time getting my glaze to absorb on the edges of my
>porcelain bowls. I'm trying to achieve a fragile shell-like form, and the
>thinner I go , the less glaze they absorb. I,ve tried bisquing lower
(010)which
>helps, but they now break in my hands when glazing. I've tried using gum and
>less water (like yogurt), and wheel brushing the glaze , but that has it's
>limitations, and shows brush-marks. Spraying is no better. Any suggestions?
>Thanks in advance.
> Joan Warren
>
>katepwa@raven.bc.ca
>sent via UUCP from: Raven Net, Salt Spring Island, BC, Canada
>

M Richens on sun 16 mar 97

In article <19970313063258382.AAA198@LOCALNAME>, Clay
writes
>----------------------------Original message----------------------------
>Any commercial glaze-maker here?
>I've been using Spectrum/Duncan dipping glaze for earthernware glazes. I
>used to have the exact problem with my plate. & the chemist of those company
>talking about adding their secret ingredients in it (instead of water. What
>it does is delay the drying time (I found) it run much slower, but it even
>out the whole body that you glaze.
>
>Actually anybody have a clue what they actually put into it?
>
Hi,

A few Ideas from someone coming from a commercial Vitreous (porcelain)
enamel background and coating steel sheet by dipping.
The problem comes down adjusting the mobility and yield points of the
slips by chemical set-up salts and by altering the type of clay in the
slip. I have mostly experience with fully-fritted production.


I won't get technical (Can't more like ) but the mobility is how the
slip flows above the yield point which is when it stops.
so
a. increasing temperature of the slip increases the mobility and keeps
the yield point the same.
b. increasing the water increases the mobility and reduces the yield
point.
c. Increase of clay content (or using a fattier clay such as a ball clay
or v-small amounts of Wyoming Bentonite0 will increase the yield value
without changing the mobility As also will adding some salt solutions.

d. grinding fineness will also change the behaviour as will the salts
which leach. High Barium containing frits can give unstable slips.This
bit is thus Suck-It-and-See Technology (TM) or use the patented Try-It-
And-See Methodology

sum up for my benefit
mobility helps the slip drain
yield point sets when it stops
for thin ware you would like high mobility to get a good beadless drain
and high yield point so that it holds on the edges and doesn't secondary
drain with unwanted beading (Have I got this right?).
So my answer would be
1. try increasing the clay or using a portion of clean Ball-clay to
replace a bit of china clay. (Bentonite can be a bit fierce in setting
up and carry a bit of lignite)
2. Try adding a very small amount of say Magnesium sulphate (Epsom
Salts) or Calcium Chloride solution to the slip. you are looking at a
ml or two of a 15% solution to a litre of slip here.
TRY A TEST FIRST not with your master slip. always set a little and mix
back
again I apologise for stating the obvious.
Other salts to try could include Potassium Carbonate, Sodium Nitrite
(not NitrAte) or Sodium Aluminate. They all react differently some could
send your slip into a thixotropic jelly or make all the fine particles
floc for a while I don't know the slip make-up.
SOME of these chemicals can be ALKALINE and the solutions in quantity
should be labelled and put on a high shelf. The small quantities in the
slip should not make an appreciable difference.

Hope this Helps
If anyone has any comments or can correct me due to my lack of
familiarity with glaze slips please do so as I'm happy to learn.

Max

PS Some of the above is from A I Andrews 'Porcelain Enamels'. Not
availably in the UK for years. Does anyone have a spare copy of a late
edition (2nd.->) for sale?
M
--
Max Richens max@richens.demon.co.uk
+44 (0) 1925756241
Enamel Consultant - Ceramist - Analyst programmer
Software for Batch Formulation and Millroom control.