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



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High Street Gallery

An example of my dry glazes

This is my
Helios Pot 2009 about 18 inches tall.
I work with slabs and roll the clay around any suitable form covered with many layers of newspaper.I add the detail from previously made moulds.My glazes are dry calcium matt glazes.Fired to 1285 o C in an electric kiln.

Dedication and Muddle; it gets worse

You got to be dedicated to do this stuff

Me in my glaze room,I am currently working on another triaxial for Shiny Cobalt greens..I am making a triaxial of Tile 2 ( FLUXT CAO_MGO_LIO__#2)and trying to identify whether it is the Ratio of the Colourants that change Cobalt from Blue to green or Titanium changing it from yellow to Green and OR whether it is the glaze base and interchangeable fluxes as shown in previous triaxials.
Here are the 3 corners of the triaxial

The Ceramic Chicken was made by layering thin pieces of textured clay, I made moulds of unusual textures using Latex.

 

High fired stoneware in a gas kiln

High fired stoneware..I wrap large pieces of slabbed clay around cardboard tubes and place on slab of clay and remove cardboard,it helps to have sheets of newspaper on the tube to ease removal and when firm enough remove tube and shape with a damp piece of chamois leather.

Generally with this colour combination of Cobalt/Rutile calcium needs to be present to obtain some Blue otherwise it changes to green or grey with magnesium and lithium present

From Corner C to B is a line blend of Lithium (C) and Magnesium (B)
This line blend contains no Calcium and has the colour has muted pale Blue at Corner B(T16) The colour in this line blend progressive from very opaque Blue grey to some beautiful shinier greys @ tiles17,18 and 19.and onto a shiny green as it interacts as the Lithium increases and the surface deteriorates at Tiles 20 and 21.Lithium seems to be a valuable secondary flux in smaller proportions adding melt and unusual colour but is not so useful in larger amounts.

From Corner A to Corner C is a line blend of Calcium (A) and Lithium (C)
Again Cnr A(Tile 1) is a Shiny Dark blue green and well melted which quickly changes to a lighter blue green variegated glaze when small amounts of lithium are introduced at T3.The tiles still remain shiny and well melted through to Tile 21.Changes to colour and texture are quite obvious along this line blend and Blue changes to apple green at T6 pinholing starts at T6 and progressively starts to melt and move.Lithium is known to produce bubbles in the glaze melt .At Corner C(Tile21) the glaze has shivered due to the small molecule size of Lithium that causes it to be mobile and it migrates to the Alumina and silica of the body and creates an interface of low expansion glass which peels off.Tile 3 is very beautiful and worth pursuing and developing.The others in the Lithium Line blend have lovely colour but the texture and surface are mostly marred by pinholing or shivering

More on Search for shiny Cobalt greens

General Observations of this triaxial Glaze are.
The glaze is a mostly stable and shiny glaze except at 2 corner Tiles A and C where the fluxes of Calcium and Lithium are predominant and Lithium has become fluid. Corner B is Matt. magnesium. The Blue green colour changing from Dark blue at Corner A to Pale blue at Corner B and Aqua green at C.




From Corner A to Corner B is a line blend of Calcium and Magnesium.
At Cnr A where Calcium is predominant the Glaze is very shiny well melted and Dark blue green it has started to move on the back of the tile this line blend progresses towards Cnr B with Magnesium becoming predominant and the surface has become more muted and becomes opaque.caused by the excessive magnesium.This line has no Lithium in its make up but has remained shiny except T16 and has no crazing.Tiles 1-11 are very interesting glaze tests.
My Colourants were Cobalt Carbonate 2.% and Rutile 6%.

Triax CaO_MgO_Li2O Cobalt Green glaze

Triaxial analysis of FLUX Triax CaO_MgO_Li2O Cobalt Green glaze.
Fired to Cone 10 in Oxidation on LF18 white firing Clay

KNO_CaO Fritt Line Blend

This line blend is exchanging KNO for CaO with Tile A with the most Calcium present and Tile B with the most KNO present.
B2O3 is present as is Alumina and Silica at constant levels. This set of tests have yielded some well melted and slightly fluid results.The colour has a definite pattern of being very strong greeny blue at Tile A and changing to an apple green at Tile B where the KNO becomes more dominant.Generally the tiles have remained shiny due to the Boric oxide adding glass to the matrix, and lowering the maturing temp.It may also have an influence
on colour in the background as it acts as a solvent and disperses colour

KNO_LiO2

This Flux combination of Li2O and CaO has interesting colour changes Shiny durable surface..where Calcium is present and as it decreases and the Lithium increases the surface becomes less shiny and the colour becomes a mossy green.and a dull surface.The surface becomes less durable as it increases with the lithium until it finally shivers off the test at tiles 2-A
Tile 6 stands out as being very different and has a beautiful depth of colour and a non crazed durable surface.I would like to test this combination further for my Cobalt green Glaze project.it seems that tile B and six are very different colourwise. Tile B Has Calcium only and turned blue and does not have any lithium in it. Tile 6 has Calcium and some Lithium and it seems that Lithium helps turn cobalt green .of course it still maybe a thickness of application. but it does have exciting connotations.

KNO__ZnO

This flux combination has KNO decreasing and ZnO increasing from A-B.
Generally this combination has produced shiny viscous glazes moving towards a matt opaque surface which has cracked and likely to peel off caused by the excess of Zinc Oxide which has a a low COE..It has also suppressed the Cobalt Carbonate allowing the Rutile to be more active.creating a more yellowish colour moving to a pale green as it has become matt. In the earlier samples the glaze has a very strong durable shiny quality Tile 5 is still shiny but has started to crawl

KNO_SrO Line Blend

This line blend consists of removing Potassium and adding Strontium.This Combination of Flux created a very inconsistent pattern of texture with very rough ,bubbly unpleasant and shiny to smooth and onto dull and matt. Where the surface quality of the tests were smooth the colour was a bright blue, tiles T3-T6 the Tiles A-2 were coarse and variegated showing some bright green Tile &B was a dull matt with a greenish hue. As a dominant flux produces eventually a matt surface. These fluxes combined are both strong fluxes and their combined fluxing power may have caused the rough bubbly surface and as the power of the flux was decreased with the KNO reduction the glaze smoothed out to eventually become matt and colour suppressed.

Line Blend of KNO_MgO

This Line blend consists of Magnesium replacing Potassium and Sodium.Generally the Colour was muted and the surface moved from shiny opaque to very matt and opaque the colour decreased as the magnesium increased There was no Crazing present and the glaze had a thick glutanous and viscous surface. Magnesium has a low fluxing power and as the amount of MgO increased towards tile 7 the glaze melted less and had less tensile strength and started to flake off tiles 6 and 7,Could also be to do with less shrinkage as well as it has a low coefficient of expansion

In search of Shiny Cobalt Titanium Greens

Line blend shows Calcium Oxide replacing Potassium and Sodium (KNO)


with Alumina and Silica remaining constant...
Cobalt Carb 2% and Rutile 6% is added to all tests.Fired to Cone 10 Oxidation.

Back view of BLC Blue green Quadraxial

Interesting this Glaze was fired in oxidation to Cone 10 but I got some lovely pinks from Cobalt.

Quad blend for Cobalt green

BLC.Blue Green
PotashFeldspar 40.00
Dolomite 9.00
Whiting 15.00
Silica 11.00
NZ China clay 25.00

Cobalt carb 1.00
Rutile 8.00

Unity Formula:
KNO 0.224
CaO 0.647
MgO 0.129

Al2O3 0.509
SiO2 2.648

The overall trend of the grid shows that as the Alumina (Amphoteric)decreases from Corner A towards corners B,C,D the Texture and surface quality becomes more glassy as the silica increases until it reaches a Silica overload at Corner D and there the surface becomes rough and sugary but still reasonably shiny. There was an almost visible diagonal divide from Corners B and C with the drier more matt surfaces closer to A and the shinier glossy surfaces closer to D..The driest most matt tile is Corner A T1 the colour is dull and grey green and the surface is scratchy to touch…The tiles become progressively less matt T21 and T26 have pink crystals in a green background where the glaze has moved and become more shiny and fluid towards Corner C T31 become beige and cream colored with some skyblue crystals in the molten glaze.

Colour wise also the deeper more interesting colours,blues around T18 and T19 Pinks around were present moving towards D as the silica content increased also and Alumina decreased. T23,24,25,28,29,30,34 and 35.T35 where the silica levels were highest the Pink became metallic where the glaze was thick and where thin, rough,sugary and grainy and a watery shine and dark green. I think that the pink comes from Cobalt when it is in an alkaline glaze and Rutile tends not to produce colour when in an alkaline glaze(Steve Ogden, potters palette)hence the colour changes as the flux oxides become more predominant at the reduction of Silica and Alumina.

The Alkali flux balance can change in the glaze melt as the silica (Acids) levels change in the Quad blends.posssibly changing the PH levels and affecting the colourant responses.

There were some very interesting colour variations caused by a change in the balance of flux and Al:Si mols around 14,15,18 and 19,allowing the cobalt to become blue,suppressing the rutile influencing factor…perhaps!!! I found that the Al;Si ratio was not necessarily a a guideline indicator to glaze quality or colour as I found two tiles with similar Al:Si ratios T8 and T31 both of which have an Al:Si ratio of 6.049. Tile 8 has a higher clay content with Al @ 0.601 and Si @ 3.637 and it had a semi matt dull dead looking grey green colour while tile 31 has no clay or silica added in the recipe and its Al mols sit @ 0.232 and Silica @ 0.401 and has the same Al:si ratio, its surface is the most fluid and has a semi matt crystalline surface which has run at the back forming sky blue glass with pinks and beige..As for colour I have 2 tiles 14 and 15 with Al:Si of 8.457 and 10.914 which are green/blue but have higher Alumina and lower silica.and showing no sign of pink and I have tiles 23 and 24 which are going green/pink. But have lower alumina levels. And higher silica levels.

Also tile 19 and Tile 28 have similar Al:Si ratios of 9.484 and 9.384,one is pink and one is blue.

So the more consistent guideline is the actual amount of mols of Alumina and Silica

Tile 18 would make an interesting stable functional glaze giving nice semi translucent forest greens and royal blues.depending on the thickness of the glaze with a tinge of pink as well. And would be worth pursuing with some line blends.etc. Also for non functional glazes it would be fun to do some tests on tiles 31-34, trying to get the pinks in oxidation and safe non volatile colour as well.The best rutile/Cobalt greens,11,12* 16,21 and 22.

The clay content also made handlebility easier and the glaze became consistently more difficult as the Alumina decreased. Not just in suspension of the glaze for mixing but also in application as well.

My overall thoughts are that the Alumina levels are the ones that control the colour the most as the only white beige tiles were in the area of 31 where there was no added clay and 26 where there was low clay.that may have some thing to do with alkalinity of the fluxes and the ph of the glazes but that hasn’t been tested here.The response of colouring oxides in a glaze melt may be different when taken up by Al2O3 and SiO2 available and different from the flux dominated overload around tile 31.

The Flux overloads of tiles 31 may allow the colourant oxides to precipitate out of the glaze melt as the glaze cools and a possibility of crystal seeding where there is an overload.