Sunday, 16 August 2009

Search for Shiny Cobalt greens

Triaxial T2 Cobalt Green fired in close formation to Cone 10 oxidation

This blend has been designed for colour; my colourants were Rutile and Cobalt.

Generally the surface quality was semi matte to shiny.The trend was that it became more shiny towards corner C which had Cobalt Oxide at 3% and which probably gave some extra fluxing power and more matt towards Rutile in Corner B at 10% which has an opacifying and matting action in larger amounts.In Corner A the glaze was shiny with a combination of Rutile 6% and Cobalt 1%.The glaze had no crazing but has pinholing and pitting throughout the whole test but Tile 5 is not so bad which could be some external factor like position in kiln and the firing or the actual combination of Fluxing power of Cobalt and stiffening action of Titanium.Also this glaze has high levels of Calcium Oxide provided by whiting which could cause bubbling from Co2 so finding a different source might be useful.

The overall pattern of colour was to move from a Pinky Grey at corner B to Dark blue at Corner C and to Green Blue at Corner A. There were some lovely greens around tiles1.58,13 and 18.Which were very similar colour combination. All had a range of Cobalt 1.00 % to 1.40% and Rutile of 5.20% to 6.00%.

It seems that the right combination of rutile and cobalt consistently give Shiny Greens of varying shades when the flux oxides and Alumina and Silica are constant in the right base glaze..

These Glaze tests have been worked out on Matrix..

Matrix software has been designed by Lawrence Ewing my tutor at Dunedin School of Art



  1. Hi;
    I am doing an independent study and instructor wants me to find a good matte glaze and a good shiny glaze. Then I am to do a line blend of the 2 to see how they change. I wonder if you could suggest 2 simple recipes- the ones I tried were too complex and didn't mix well... turned into concrete practically on bottom of containers. I wonder if you did this test at some point in your learning.
    Thanks Jody

  2. Hi Jo..I am very sorry that I did not come back here until now and probably too late..depending on what temp and what atmosphere you fire in..but I find Emmanuel Coopers book of glaze recipes reliable and it also has substitutions of materials so depending where you are..
    I fire it to cone 9 Electric but there are so many variable like ramp and soak so what works for me may not work for of luck..let me know how you got on.
    I use 169 soft semi matt drier over stoneware.
    169 E COOPER C6-10

    Cone 10 1285 deg.C. -

    Potash Feldspar 200FPR 30.00
    Nepheline Syenite 200 10.00
    Whiting 30.00
    Ball Clay FX 30.00

    Seger Weight%
    KNO 0.196 7.20%
    CaO 0.803 20.42%
    MgO 0.001 0.01%
    Al2O3 0.421 19.46%
    SiO2 1.922 52.35%
    TiO2 0.015 0.55%
    K2O 0.115 4.92%
    Na2O 0.081 2.28%
    Al:Si 4.56
    Expan. 12.40
    ST 389.12

    Drier sculptural glaze.Has been good with copper.

    Janet DeBoos
    JDB 82 CLEAR

    Cone 9 1260 deg.C. - Ox. or Red.

    Potash Feldspar 200FPR 25.00
    Whiting 20.00
    Silica 35.00
    Ball Clay FX 25.00
    Ferro 4108 10.00

    Seger Weight%
    KNO 0.202 4.51%
    CaO 0.798 12.55%
    Al2O3 0.402 11.47%
    B2O3 0.097 1.89%
    SiO2 4.108 69.21%
    TiO2 0.016 0.37%
    K2O 0.111 2.93%
    Na2O 0.091 1.58%
    Al:Si 10.23
    Expan. 8.62
    ST 357.75

    Clay Body
    Glaze Type
    Opacity Clear
    Texture Glossy
    Stability No Movement
    Fit Primary Crazing
    Last changed: 24/04/2008
    Status Tested
    Good with stains