Martha Muzychka on thu 25 apr 96
Here are the glaze test results I promised last week. All are cone 6
oxidation glazes (note I used the new orton cones). All were tested on
ridged egg cup forms using a creamy white stoneware clay (Pottery Supply
House). Some tests I also tried on black stoneware clay. If anyone has any
recipes or sources I might try for glazes that work with black stoneware,
I would be very grateful.
Gerstley Borate 50
Chrome Oxide 1
Cobalt Carbonate 1
This turned out really well -- nice gloss, good fit, and smooth
The original poster (Maria?) posted that this made a good base glaze so I
also tested it with the following colorants:
Black Iron Oxide 2
Chrome Oxide 2
Cobalt Carbonate 2
I got an interesting black. Where it is thick, there are spots of dark
blue floating over a soft black. Where it is thin it is a very dark green
black (like a mussel shell). I will probably try other colour combinations
to see what happens.
Floating Blue Glaze
Nepheline Syenite 47.3
Gerstley Borate 27.0
Red Iron Oxide 2.0
Cobalt Carbonate 2.0
CMC 1 tsp
This was a not what I expected. It wasn't runny but it was mostly green
with a few spots of blue. I will resieve it and see what happens. I also
tested this over black stoneware clay, and it gives an unusual cloudy
Gerstley Borate 26.0
Copper Carbonate 5.0
Red Iron Oxide .5
This is a clear high gloss leaf green, darker where it has pooled. It was
best when dipped (looked very splotchy when brushed).
Custer Feldspar 50.0
Zinc Oxide 10.8
Cobalt Carbonate 2.5
I really liked this glaze. I mixed up a 5000 gram batch, which I sieved
twice (once at 80 and once at 100). This has a lovely silky feel, and it
looks great on my bottles. The colour is a nice olive green, mottled, and
dark blue where thick and/or pooled.
Nepheline Syenite 56.18
Red Art 13.48
Magnesium Carbonate 4.49
Zirconium Silicate 12.36
Red iron Oxide 6.74
This has a smooth satin finish, a bit dry if it is very thin. It is a
creamy yellow tan where thick with dark red underneath. I mixed up a
second test and used 5 per cent RIO and it looked quite nice. This did not
look very nice over black clay -- very dull and dry looking brown red.
Custer Feldspar 37.34
Zinc Oxide 2.70
Cobalt Carbonate 1.75
This was a surprise. The colour was Easter egg purple, satin surface with
a good fit. I was a bit shocked by the colour but then read that 3.3 CC
should be used to get a dark purple.
Kemp 5 Soft Green or Blue
Nepheline Syenite 67.0
Zinc Oxide 6.0
Copper Carbonate 3.0 for green
Copper Carbonate 1.5 for blue
Cobalt Oxide .25
The soft green was not nice at all. It was very pale and had brown streaks
instead of pink. The blue was better in colour, but it also breaks to an
icky greyish brown where thick.
Next week I'll post the results of the white glazes.