Sunday, 29 November 2009
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