Don Penny on sat 19 nov 05
I have an interesting problem that I cannot explain, and hope somebody can
shed some light, maybe come up with a solution.
I have been using a particular cone 10 stoneware glaze for 40 years without
a problem. It is a common glaze in studio potteries, being known by various
names, CB40, HCM (High Clay Matt) etc. Fires to a nice satin matte at cone
9-11.The recipe is:
potash feldspar (G-200)......48.9
kaolin (EPK)............25.2
dolomite (Camadil).......22.4
whiting (Imery no.10).........3.5
When I mix this glaze it gets a foamy scum on the surface, lots of bubbles
entrapped in the glaze proper. The entrapped air bubbles are very small, but
do not leave, and render the glaze unsuitable for dipping. The glaze must be
rubbed smooth by hand to prevent pinholes or craters. It sprays just fine.
Another glaze of a similar composition did the foaming, too.
My question is whether anyone else has experienced this. Sometimes materials
DO change. This has never happened before. As you see, the materials I'm
using are very consistent. My mixing water COULD be suspect. A separate
batch mixed with another water source did NOT foam!
I do use a deep well for untreated water, and it certainly is possible that
the quality has changed, though not likely. I am having the water tested
next week for bacteria, VOC (volatile organic contaminants) and
hardness,(usually iron, magnesium and calcium).
Has anybody any knowledge about water quality impact on glaze mixing? Does
hardness of water matter? Maybe algae or bio-contamination?
Mail direct to my email at dpenny@alltel.net
Thanks all
Don Penny, Little River Studio
Gordon Ward on sat 19 nov 05
I have had this happen, but it usually goes away after sitting. I have
thought that high clay content is the culprit. I haven't tried it, but
spraying a bit of alcohol on the surface may help break the surface
tension.
Gordon
On Nov 19, 2005, at 1:04 PM, Don Penny wrote:
> When I mix this glaze it gets a foamy scum on the surface, lots of
> bubbles
> entrapped in the glaze proper. The entrapped air bubbles are very
> small, but
> do not leave, and render the glaze unsuitable for dipping.
earlk on sat 19 nov 05
Don,
Sounds like your water may be acidic and reacting
with the carbonate in the dolomite and whiting to
produce tiny bubles of CO2. You could get a
swimming pool pH test kit to check this.
If the water is acidic maybe a pinch of soda ash or
baking soda in the water before you mix in your
glaze components may raise the pH enough to
eliminate the problem. Or mix a little of the
whiting in the water first and let set a day before
adding in the rest.
This is just a SWAG (Scientific Wild Ass Guess).
earlk...
bothell, wa, usa
John Britt on sun 20 nov 05
Don,
You might try mixing the glaze up with distilled water. See if it
happens. If not, it may indicate that your water is, in fact, the
problem.
You could, then, always mix that or all your glazes with distilled water.
It will eliminate one variable and is not that expensive of a cure.
Hope it helps,
John Britt
www.johnbrittpottery.com
Lee Love on sun 20 nov 05
On 2005/11/20 6:04:24, dpenny@alltel.net wrote:
> When I mix this glaze it gets a foamy scum on the surface
Don,
I would recommend "washing" the glaze. Washing should not effect the
original nature of the glaze, because it doesn't seem to depend upon
solubles.
Put the glaze in a larger container. Fill with water, preferable from a
source you can trust. Leave enough room at the top of the trashcan or
bucket so you can stir vigorously with an electric mixer. After the
glaze has settle, scoop, pour or siphon off the water and bubbles at the
top.
Repeat this procedure until the bubbles are gone.
--
李 Lee Love 大
愛 鱗
in Mashiko, Japan http://mashiko.org
http://seisokuro.blogspot.com/ My Photo Logs
http://ikiru.blogspot.com/ Zen and Craft
"We are such stuff / As dreams are made on, and our little life / Is
rounded with a sleep."
--PROSPERO Tempest Shakespeare
Des & Jan Howard on sun 20 nov 05
Don
Some of my glazes foam, they may have either CMC gum or PVA glue added
to them, one or two with no additions.
The foaming is cleared with a couple of squirts from a plastic spray
bottle containing 2 parts water-1 part methylated spirits.
Des
Don Penny wrote:
>When I mix this glaze it gets a foamy scum on the surface, lots of bubbles
>entrapped in the glaze proper. The entrapped air bubbles are very small, but
>do not leave, and render the glaze unsuitable for dipping. The glaze must be
>rubbed smooth by hand to prevent pinholes or craters. It sprays just fine.
>Another glaze of a similar composition did the foaming, too.
>
>My question is whether anyone else has experienced this. Sometimes materials
>DO change. This has never happened before. As you see, the materials I'm
>using are very consistent. My mixing water COULD be suspect. A separate
>batch mixed with another water source did NOT foam!
>
>
>
--
Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.hwy.com.au
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