Cindy Strnad on fri 21 jan 00
------------------
Hi, Everybody.
I have a pretty =5E6 glaze called Honey Amber which, if I remember right, I =
picked
up from CLAYART some time ago. It's actually more of a tobacco juice color,
unless you cut the MnO2 in half. Though I like the look of it, I hadn't used=
it
much until recently when I discovered that one of my other glazes looks =
gorgeous
when trailed across it. I'm noticing now that it pinholes sometimes and =
would
like to fix this. Here's the recipe.
Dolomite 20
Frit 3134 20
Spodumene 20
OM =234 20
Silica 20
Plus Manganese Dioxide 3
Red Iron Oxide 5
Okay, now here's where I stick my neck out a bit . . . I really am trying to
understand this glaze chemistry thing, but if I sound totally off the wall,
please forgive me.
The understanding I have is that pinholing is caused (if not by dust or an
under-fired body) by bubbles which cannot escape because the glaze melt is =
too
stiff. This is really a quite glossy glaze already, but if fixing it makes =
it
glossier, I don't think that will detract from its appearance. I don't have
trouble with it running off the pots, although that may be because I always
apply it thinly.
It's below Insight's limits for potassium and sodium, but I'm guessing the
lithium makes up for that? Or do I need to increase the fluxes? The silica =
is
also slightly low, though the alumina is in the middle of the suggested =
range. I
wondered if increasing the silica would help and tried that, but bringing =
the
silica up to around 3.0 decreases the expansion so much I'm afraid the glaze
would shiver on my stoneware clay. What should I try?
One thing I really like about this glaze is it's clarity. The other thing I =
like
is the way my blue glaze, when trailed over it on a flat surface, blossoms =
out
into blue 'flowers' edged with green and purple. These are the qualities I'd
like to keep.
Thanks in advance for your help,
Cindy Strnad
Earthen Vessels Pottery
Custer, SD
David Hendley on tue 25 jan 00
I didn't see any responses to this, Cindy, so here
are a couple of ideas you might try.
First of all, try using the same molecular formula, but,
using your glaze calculation program, use different
materials.
The idea is to use things with less volatility because
as things burn away they can leave pinholes.
I would suggest getting rid of the dolomite, replacing
it with magnesium carbonate (magnesium) and/or talc
(magnesium and silica), and wollastonite (calcium and
silica).
Also, use EPK instead of ball clay.
(For others who might be reading, a glaze calculation
program is necessary to make these substitutions,
because these are not direct one-to-one substitutions)
Next,if that doesn't help, try varying the fluxes.
Maybe increase the KNaO at the expense of the
lithium - the resultant look should be similar.
Try adding a new flux. Clayarter Dave Cuzick has
had good luck adding zinc oxide, as an extra flux,
to a glaze was prone to pinholing.
Goodluck,
--
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com/
----- Original Message -----
From: Cindy Strnad
To:
Sent: Friday, January 21, 2000 12:16 PM
Subject: Honey Amber Glaze
----------------------------Original message----------------------------
------------------
Hi, Everybody.
I have a pretty ^6 glaze called Honey Amber which, if I remember right, I
picked
up from CLAYART some time ago. It's actually more of a tobacco juice color,
unless you cut the MnO2 in half. Though I like the look of it, I hadn't used
it
much until recently when I discovered that one of my other glazes looks
gorgeous
when trailed across it. I'm noticing now that it pinholes sometimes and
would
like to fix this. Here's the recipe.
Dolomite 20
Frit 3134 20
Spodumene 20
OM #4 20
Silica 20
Plus Manganese Dioxide 3
Red Iron Oxide 5
Okay, now here's where I stick my neck out a bit . . . I really am trying to
understand this glaze chemistry thing, but if I sound totally off the wall,
please forgive me.
The understanding I have is that pinholing is caused (if not by dust or an
under-fired body) by bubbles which cannot escape because the glaze melt is
too
stiff. This is really a quite glossy glaze already, but if fixing it makes
it
glossier, I don't think that will detract from its appearance. I don't have
trouble with it running off the pots, although that may be because I always
apply it thinly.
It's below Insight's limits for potassium and sodium, but I'm guessing the
lithium makes up for that? Or do I need to increase the fluxes? The silica
is
also slightly low, though the alumina is in the middle of the suggested
range. I
wondered if increasing the silica would help and tried that, but bringing
the
silica up to around 3.0 decreases the expansion so much I'm afraid the glaze
would shiver on my stoneware clay. What should I try?
One thing I really like about this glaze is it's clarity. The other thing I
like
is the way my blue glaze, when trailed over it on a flat surface, blossoms
out
into blue 'flowers' edged with green and purple. These are the qualities I'd
like to keep.
Thanks in advance for your help,
Cindy Strnad
Earthen Vessels Pottery
Custer, SD
Stephen Parry-Thomas on wed 26 jan 00
In a message dated 1/25/00 7:26:44 PM GMT Standard Time, hendley@tyler.net
writes:
Cindy,
I have a honey glaze that we used at the Gladstone Pottery Museum, Longton,
Stoke-on-Trent, Staffs., UK it goes like this
Red clay 3 lb.
Yellow Iron Oxide 12 oz
Flint 1 lb.
Lead Bisilicate 20 lb. or a lead fritt .
I have not used this for some years, I tend to add about 5% iron oxide to a
clear glaze these days. I'm just getting lazier and older!
Stephen Parry-Thomas.
www.morrigancraftpottery.co.uk
Stephen Parry-Thomas on fri 28 jan 00
Just a reminder about to use of lead compounds and fritts in the UK.
It is a mandatory requirement for domestic wares to pass the British Standard
(B.S.) 6748 Parts 1 and 2.
BS6748 Part 1 1972
Flatware - lead = 20 ppm (pans per million)
Cadmium = 2ppm
Holloware - lead 7ppm
Cadmium = 0.2 ppm
Storage vessels or any holloware over 1100 milliltres capacity
lead = 2ppm
Cadmium = 0.2 ppm
The test involves exposure to 4% acetic acid (vinegar) at room temperature
for 24 hours. Holloware is defined as "any artical in which the ratio of
height to diameter is equal to, or exceeds one half. Flatware, - plates
saucers and dishes.
BS6748 Part 2 1972
Refers to cooking wares. oven-to-tableware. The test is the ceramic item is
exposed to boiling acetic acid for two hours followed by a cooking period of
22 hours. The limits are
All shapes - lead = 7ppm
Cadmium = 0.7 ppm
Never ever mix copper oxide with lead glazes or fritts. The lead glazes I are
used on garden terrcottaware for outside use and not for domestic use.
Stephen Parry-Thomas
www.morrigancraftpottery.co.uk
old potters never die they just kiln themselves
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