hal mc whinnie on mon 14 aug 00
ONLINE GLAZE COURSE, LESSON eight PART ONE
Some non-traditional glazes and the question of feldspar substitutes
FELDSPAR SUBSTITUTIONS
Oxford feldspar
There will be no more so in formulas, which call for oxford use Custer
feldspar in
proportions
Soda feldspar f-4
When you wish to have feldspar high in soda, use neph syenite. This will
tend to make
the glaze mature at a lower cone level. In fact when you substitute NEP syn
for another
feldspar such as Custer you lower the maturing point of the glaze by about
two cones
Potash feldspar a3
When you wish to have feldspar high in potash use either Custer or
Cornwall.
Custer has a chemical analysis very similar to a-3 and can be substituted
for it in a glaze
formula
If you substitute Cornwall stone the glaze should be fired at a cone higher
in
temperature.
You can also substitute Buckingham feldspar for a-3 potash; this
substitution
should however cause the glaze to mature at a cone lower in temperature.
MATERIALS FOR PHOTO-SENSITIVE CERAMICS
A] Photo-sensitive luster glaze
Ferric ammonium atrate 21.25
Tartaric acid 3.5
Silver nitrate 9.0
Water to make 250cc
Mix sensitizing solution in dark room and keep in airtight amber bottle
Base glaze
Frit 3195 810 g
Ball clay 90 gms
1] Glaze can be precalcined onto surface. Add enough water to make glaze
consistency
onto surface. Add enough water to make the glaze consistency and paint onto
flat
surface, let dry. In a dark room, paint the sensitizer, dry, expose, and
rinse.
2] Mix sensitizer and glaze- 1/4 dry wt. Sensitize to 35-50 pts base glaze
use
immediately unless stored dry and light tight.
Firing begins reduction at 800 for 30 minutes, medium heavy, maintain at
least a
neutral flame.
Flash luster is with metallic salts added directly to the glaze, cool with
reducing
atmosphere or neutral
PHOTOSENSITIVE GLAZES
OXIDATION
1/2%COBALT CARB FOR MEDIUM BLUE
4%COPPER CARB FOR STRONG GREEN
I/2 COBALT AND 2%$COPPER CARB FOR BLUE GREEN
6%VANADIUM FOR MEDIUM YELLOW
3%COPPER CARB AND 3% VANADIUM FOR YELLOW GREEN
5%VANADIUM AND 4% RUTILE FOR WARUM OCHRE
BASE GLAZE FOR ABOVE COLORS
FRIT 41 95 AND BALL CLAY 5 FOR CONE 011
FRIT 33004 144
FRIT 9P1733 16
EPK 20
FOR CONE O4
[YOU CAN PROBABLY SUBSTITUTE FRITS 3124 AND 3134]
LITHIUM CLAYS FOR OVEN PROOF WARE
Lithium body one
Cone 9
Spodumene 40
] Fireclay 20
Cedar heights redart 10
Ball clay 20
Redfire clay 10
Lithium body two
Spodumene 30
Fireclay 20
Bonding clay 10
Fine grog 10
Sager clay 30
Glazes for ovenware clays
Alfred white Matt [cone 9]
Potash spar 26
Spodumene 17
Dolomite 21
Whiting 3
Epk 22
Magnesium silicate 8.9
GLAZING WITH Portland CEMENT
1] Portland cement has about the same composition as a cone 10 glaze. When
used
over a variety of oxides it produces some very interesting surfaces and
glazes
Oxide mixtures for slips for cement glazes
Manganese 2 parts
Red iron 1 part
Cobalt oxide 1
Oxide mixture two
Black nickel oxide 1 part
Red iron oxide 2 parts
White slip for cement glazes
Epk 30
Ball clay 25
Feldspar 20
Flint 15
Zircopax 5
Borax 5
CRATER GLAZES
Otto natzler pioneered in the use of corbordum a silicate used for grinding
for an
additive to glazes. 10% will produce a moderate texture in almost any glaze
30-50% will produce very rough lava like texture.
The use of small amount in glazes for oxidation in an electric kiln will
produce copper
reds.
The reason is that the corbordum grains keep the glaze materials from
flowing at any
cone level and the glaze and gases erupt around each particle very much like
lava.
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