Cobalt Titanium Green Vases

A few examples from some of this years tests.

This test was set up because I suspect that the Alkali/Acid ratio in this test is only part of the equation. A 1.4 ratio can produce Greens and Blues from Cobalt and Titanium depending on the levels of Alumina.According to Frank Hamer “Ampohterics can act as an acid or alkali depending on the base formula and they are an interface between the two”.
This test has Alumina Decreasing from A to B and Alumina increasing from B to C .
KNO increasing from A to C and Calcium increasing from C to A whilst silica and Colourants remain constant.
I had hoped to show that by leaving the Acid /Alkali ratio of 1:4 it would change a Shiny Cobalt green glaze to Blue. Generally the surface quality goes from shiny translucent towards opaque there are considerable pinholing problems as it moves towards 16 and 21. and adjustment to Titanium levels with correspondent Cobalt levels ie 1.20 CoO and 5.60 TiO2 and a possible change in CaO source like wollastonite etc might help also experimenting with firing etc.
Corner A to C….I have found that CaO is an important factor in Cobalt Green glazes and I had hoped also to show that be exchanging KNO for Calcium that it would have an affect on colour too.@ A to C it has changed from a lovely transparent green to transparent blue and finally to a semi shiny Opaque Blue with Pink tinges.

Corner A to B this line blend has Alumina decreasing from A to B again a shiny translucent green tile @ A 1 progressing to translucent Blue to an Opaque Sky Blue with a rough sugary surface.

Corner B to C.
This line Blend has the lowest alumina levels at B and increasing to C. B has the same KNO and CaO levels as A but CaO decreases towards c and KNO increases towards C which give C the highest KNO and Lowest CaO at C21. this line blend changes in colour from a bright opaque sky blue at B to a paler opaque blue at C which is the palest colour of the whole test..

My conclusion for this test is that at an Acid/Alkali ratio of 1 to 4 shiny translucent greens can be produced but the critical factor is how the Amphoterics will behave in the glaze matrix.
Too much KNO and not enough CaO turn it from Green to a pale Blue.
With the right balance of flux CaO predominant,the reduction of Alumina will affect the colour as it decreases and also turns the green to blue.

Even with an acid /Alkali ratio of 1:4..I can say with the right balance of Flux and the wrong balance of alumina you still wont produce green and with the wrong balance of flux and the right balance of alumina you still wont produce green.
Hence it is not just the Flux:Silica Balance..it is also the Flux ,Amphoterics and Colourant balance needed to produce Cobalt green..and there is a small window of opportunity for Shiny translucent Cobalt Iitanium Green I suspect.

Tests on KNO_CaO Tile 6 Plus and Minus Clay.

This line blend has been designed to show the influence of Alumina and Silica on a Cobalt Green Glaze to see the development of Blue.
The original tile KNO_CaO T6 formula was Alumina 0.517 and Silica 4.113.The KNO and CaO and colourants are constant.

In this line blend as the Alumina and Silica have increased from A towards B the colour has changed from a bright semi matte Blue to Shiny dark blue to shiny green to semi matte dull green to a pale dull matt green at the highest Silica and alumina levels Tile 7B. The Alkali/acid ratio has increased from 1:3.588 to 1: 4.639 and the best green has to be Tile 5 at a ratio of 1:4.215.
To me this test shows that if the CaO and KNO levels are correct greens can be produced BUT it is more than the Acid/Alkali ratio that makes green.Alumina also plays a large part in making of Green or Blue and these levels play a crucial part in the glaze matrix.

KNO_CaO Tile 6 plus and Minus Silica.

Here in this test again the original tile KNO_CaO T6 formula was Alumina 0.517 and Silica 4.113.The KNO and CaO and colourants are constant.
And I have reduced and added Silica. Here Alumina remains constant also so the only change is in silica giving us a different acid /alkali ratio from A to B. The acid/alkali ratio starts at 1:3.080 to 1:5.147 which is Blue
The Cobalt green colour has started as a dull bluer green at A progressing towards lovely shiny greens at 3,4,5 and 6 though it is showing signs of the cobalt blue influence from 6 to 7 which is much bluer at 7B.The best green has to be Tile 4 with a an Alkali/acid ratio of 1:3.958

Still got a long way to go to find nice Iron yellow glazes

This is a line blend of DeBoos high Calcium Matt which goes from red to yellow.
I added Titanium Oxide up to 4% to see what sort of reaction I would get.I also overglazed it with a White rutile glaze of unknown ingredients..ie a bucket of slops :-)

My favourites from this Triaxial

An example of the recipes,the base glaze stays the same and the colourants vary from Cobalt 1.00 to 1.40% and Rutile 5.20 to 6.00% for the nicer greens.The blues are also good but I have been interested in green only.

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



,,,,,,,,,,,,,,,,,,,,,,,,,

High Street Gallery