Post 30 Glaze testing & recipes

Here are some of the results of my recent glaze trials; all cone 6 to 1240C.

All the glaze formulations in this post have produced a buttery soft satin matte finish with the same look and feel over the whole surface. All of them offer exactly what I'm after for pot glazes in application and finish. The colours are all muted, almost pastel variations which again are perfect for bonsai pots, not wanting to outdo the appeal of the tree!. My next series of trials will concentrate on these few base formulations with a wider gradation of colourant variations.

The first three shots are of variants of John Post's high calcium matte cone 6 glaze.

I've modified the original formula to accommodate the available local Frit and also to give the glaze that touch of satin finish I've been chasing. I also formulated a number of variants to test the alternatives.

The first set use the following base:

Nepheline Syenite        31.5

Whiting                           4.9

Silica                              12

Ball Clay                         22.6

Frit 4124                          5

Kaoliin                              8

Wollastonite                   16

The unity ratio is 5.82.

 Additions to the base glaze are:

4-1  Copper Carb 0.5%, Cobalt Carb  0.75%, Titanium Dioxide 2%, Rutile 6%
4-2  Cobalt Carb  0.5%,  Titanium Dioxide 4%, Manganese Carb  5%
4-3  Red Iron Oxide 4%, Titanium Dioxide 2%,  Manganese Carb  4%,  Rutile 6%
4-4  Copper Carb  2.25%,  Cobalt Carb  0.25%,  Titanium Dioxide 2%, Rutile 6%
4-5  Titanium Dioxide 2%,  Manganese Carb  4%, Rutile 6%


The next two have a base glaze composition of:
 
Nepheline Syenite        20
Whiting                           7
Silica                              16
Frit 4124                         5
Talc                                  5
Kaoliin                            29
Wollastonite                   18
The unity ratio is 5.93.

 

 
 Additions to the base glaze are:

4-8  Cobalt Carb  0.5%, Nickel Oxide 1.5%,  Titanium Dioxide 2%, Rutile 6% (a very attrqctive pastel green with a little Rutile speckle)
4-9  Red Iron Oxide  4%, Tin Oxide 5% (good for breaking variegation on surface relief)


The next two have a base glaze composition of:
 

Nepheline Syenite        14
Whiting                           7
Silica                              15
Frit 4124                         10
Talc                                  4
Kaoliin                            32
Wollastonite                   18
The unity ratio is 5.82.

 

 
4-10  Nickel Oxide 1.5%,  Titanium Dioxide 4%, Rutile 6%
4-11  Red Iron Oxide  4%, Tin Oxide 5%

The next two sets derive from a Digitalfire formula, (G2571A).
 
The next set, 4-14 to 4-18, use the following base:

Custer Potash              26
Whiting                          10
Silica                             15
Kaoliin                           24
Dolomite                       15
Wollastonite                   6
Gerstley Borate             4

The unity ratio is 5.9.

  
 Additions to the base glaze are:

4-14  Cobalt Carb  0.5%, Nickel Oxide 1.5%,Titanium Dioxide 4%
4-15  Red Iron Oxide 3%, Copper Carb 0.75%,Cobalt Carb 1%, Rutile 6%
4-16  Red Iron Oxide 0.5%, Copper Carb 1%,Cobalt Carb 1%,Titanium Dioxide 4%
4-17  Nickel Oxide 2%, Tin Oxide 3%, Rutile 6% (nice creamy tones when thicker)
4-18  Copper Carb 3%, Nickel Oxide 1%, Rutile 6%

And the final set base formula is;

Custer Potash              25
Whiting                          3
Silica                             20
Kaoliin                           25
Dolomite                       17
Wollastonite                   6
Gerstley Borate             4

The unity ratio is 5.9.
 

Additions to the base glaze are:

4-23  Copper Carb  4%, Rutile 6% (this was one of only a few where the Rutile provided speckling as well as just being an opacifier like Titanium)
4-24  Red Iron Oxide 6%, Rutile 6% (better colour when not too thick)
4-25  Red Iron Oxide 4%,Titanium Dioxide 4%, Manganese Carb 3%
4-26  Cobalt Carb 1%, Rutile 6%
4-27  RIO 0.25%, Cobalt Carb 1%, Tin Oxide 4%