Chris Schafale on fri 2 jul 99
Greetings all,
In my ongoing glaze quest, I've been exploring glazes in the
satin-matt to semi-gloss range, for cone 5-6 oxidation firing. In
the process, I'm running into some phenomena I'm not familiar with.
Some glazes have pinholes, which I'll define as circular, with
rounded edges, and with the hole sometimes going all the way down to
the clay and sometimes not quite that deep. So far, this is
familiar. But I've also run into glazes that have what I'd call a
"pigskin" quality -- many small indentations, sometimes elongated in
appearance rather than round, covering the surface. Still others
have an even more subtle overall texture that looks to the naked eye
something like smooth human skin, as if it had tiny pores or wrinkles
completely covering the surface.
Anyone have any theories or observations on what causes these
phenomena, and how they might relate to the oxide balance, firing
temperature, appropriateness of the glaze for food-contact surfaces,
interaction with clay body or anything else that comes to mind?
Ian Currie mentions a group of glazes that he calls "orange-peel",
and I'm wondering if some of these are what he is talking about.
(It's kind of hard to be sure because his results are based on cone
9-10). Has anyone out there done the Currie "experiments" in cone 6
ox.?
Thanks for any thoughts.
Chris
Here are some recipes for those who are interested:
Leather plus silica: This one was based on a glaze from clayart, but
I added silica to try to make the surface less dry. With the
silica, I would describe it as still on the dry side of satin. I got
the "pigskin" effect at cone 5, but confusingly, not all the time --
may happen on some clay bodies and not others? Or very dependent on
subtle changes in firing regime? When I refired a piece to cone 6,
it got shinier in thin spots, but kept the pigskin texture where it
was thicker.
===================
silica.............. 16.00 16.00%
wollastonite........ 4.00 4.00%
dolomite............ 17.70 17.70%
EPK................. 14.00 14.00%
Gers Borate 9/97.... 8.40 8.40%
spodumene........... 7.40 7.40%
custer feldspar..... 22.50 22.50%
nepheline syenite... 10.00 10.00%
========
100.00
CaO 0.46* 10.23%
Li2O 0.05* 0.65%
MgO 0.30* 4.74%
K2O 0.09* 3.29%
Na2O 0.10* 2.42%
TiO2 0.00 0.06%
Al2O3 0.39 15.73%
B2O3 0.11 2.99%
P2O5 0.00 0.04%
SiO2 2.50 59.55%
Fe2O3 0.00 0.30%
Cost/lb 0.40
Si:Al 6.42
SiB:Al 6.70
Expan 6.92
B2: This is a base glaze I made up. On this one, fired to cone 5, I
got something between pinholes and pigskin -- small, relatively
deep-looking, round holes, but all over. In between the holes, it
was fairly glossy. I thought it was underfired, but the pinholes
turned into sharper-edged blisters and the glaze ran where it was
thick when I refired the pieces to cone 6.
======
G 200 FELDSPAR...... 45.00 45.00%
SILICA.............. 14.00 14.00%
EPK KAOLIN.......... 13.00 13.00%
DOLOMITE............ 13.00 13.00%
3134................ 15.00 15.00%
========
100.00
CaO 0.43* 8.02%
MgO 0.24* 3.14%
K2O 0.17* 5.33%
Na2O 0.16* 3.18%
TiO2 0.00 0.05%
Al2O3 0.43 14.42%
B2O3 0.16 3.77%
P2O5 0.00 0.04%
SiO2 3.13 61.90%
Fe2O3 0.00 0.15%
Cost/lb 0.56
Si:Al 7.28
SiB:Al 7.67
Expan 7.48
CMB2: This is another attempt at a base glaze. At cone 6, this one
has the micropore texture, with a semi-gloss to satin-matte surface.
Quite attractive, at least on a little tiny test tile, don't know
what it would be like on a pot yet.
==================
G 200 FELDSPAR...... 33.00 33.00%
TALC................ 5.00 5.00%
SILICA.............. 10.00 10.00%
PIONEER KAOLIN...... 16.00 16.00%
3124................ 10.00 10.00%
WOLLASTONITE........ 26.00 26.00%
========
100.00
CaO 0.70* 14.60%
MgO 0.12* 1.75%
K2O 0.11* 3.71%
Na2O 0.07* 1.70%
TiO2 0.01 0.23%
Al2O3 0.36 13.55%
B2O3 0.05 1.40%
SiO2 2.83 62.96%
Fe2O3 0.00 0.10%
Cost/lb 0.52
Si:Al 7.89
SiB:Al 8.04
Expan 7.24
Light One Candle Pottery
Fuquay-Varina, NC
candle@intrex.net
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