Flat Matte Blue ^6 Recipe?

[Magnet]

Does anyone have a recipe for a stable, matte blue cone 6 glaze? Something like this...

 

[Magnet]

Here are two that I came across in an old binder in a co-op that I work at. I'll run some tests on these soon, but would like to hear if anyone has experience or reservations about these recipes. Thanks for any help.

 

^6 Oxidation Matte Blue

Nepheline Syenite        34.95
Kaolin                         17.43
Silica                            16.42
Wollastonite                12.03
Strontium Carbonate   10.68
Zinc Oxide                  5.84
Lithium Carbonate      2.65
Total Base:                  100.00
ADD

 Copper Carbonate      1
 Cobalt Carbonate        1.5

Total:                           102.50

^6 Matte Dark Blue
Custer Feldspar            45.6
Edgar Plastic Kaolin    18.4
Whiting                        16.6
Zinc Oxide                  6.4
Red Iron Oxide            4.2
Silica                            4.6
Cobalt Oxide               4.2

Total:                           100

[Min]

Couple things, first off are you looking for a fairly matte glaze for the food surfaces of functional pots like your example piece? Don’t think using a matte glaze for that is a good idea, not as chemically sound as a gloss glaze.  

 

Both glazes are a bit short of silica, first glaze needs it bumped up to 19.42 to come to the lower target level (using Insight glaze calc), second glaze needs a minimum of 8.1 silica. 

 

Zinc in the second glaze is high, need to drop that down by 1 to get to the upper end of target limits. 

 

Cobalt level in the second glaze is super high. You can get a strong blue with most glazes with about 1 - 1 1/2% cobalt carbonate (to sub the cobalt ox for carbonate for every 1 part of cobalt oxide swap with 1.53 part of cobalt carbonate,  or for the other way around substitute 1 part of cobalt carbonate by 0.653 part of cobalt oxide). 

 

If you have a copy of the Mastering Cone 6 Glazes book have a look at their high calcium matte glazes. You can fiddle with the colourants to get what you are looking for. Need to be able to slow cool your kiln to get the semi matte finish.

[Magnet]

Thanks, Min, for the feedback. 

 

The glaze will be not be used for food-functional pieces. However, I just read digitalfire's page on the dolomite matte base glaze, and I'm going in that direction. I have a lot to learn about ^6 glazes, and Insight/digitalfire looks like a great direction for me.