Tess Brady & June Johnstone

Ash Glaze Journal 2005

Clay
Slips, Engobes and Opacifiers
Ash Glazes
Firing

This work was carried out as part of a Diploma of Arts, Ceramics Arts Academy, University of Ballerat

The clay remembers the place where it was dug. We search for the coordinates 

Introduction

Coming to Ceramics

June comes from a strong music background, Tess from a writing one. As older women who have developed careers in other sectors of the arts, education, communication and tourism we approached ceramics as an extension of our already acquired skills. Neither of us expects or dreams of becoming renown potters. It is enough for us to enjoy the experience of clay, its serious and playful side and to watch as we learn new art processes and adjust the ones we already know.

The Journal
In ceramics we have learnt of the importance of the journal. How much of the thinking of the assignment is carried out in that space so that on coming to the clay attention can be given to process and technique. It is true of course that  the act-of-making generates new creative ideas but we were both interested in the way the journal functioned as the mainstay of the thinking process. As inexperienced potters in need of much attention to our processes this proved a helpful tool. It also allowed for repetition, an important aspect of a potters work. Having thought of the idea, researched it, sketched and developed it, time could be spent on making the object. Once the object was made the process can be repeated.

This is not the method used in musical composition, performance or writing.   All have aspects of research, inspiration, development, notes and the like, but they do not function in the same order or with same weight as in ceramics.

The Glaze Note Book
Glaze note taking is different again and required a scientific care to numbering experiments and recording processes and results. We quickly realised the necessity of this and to not rely upon our memories. We began recording not only the formula but also the process of application of glazes.

Further, we discovered that it was important to write up our work so that we could refer back to it. While test tiles, line blends and triaxial were used extensively as visual tools, we found we also needed to refer back to our written work and so had on hand a copy of what we considered at first to be “our assignment”. 

Our Growing Approach to Clay
Free to explore a vast range of colours and chemicals we found little interest here. Instead we quickly became engaged with the colours, textures and shapes of our landscape. We wanted to make pots and glazes from our world – digging clay and ochres, sorting ash from our fires, burning fallen locally grown trees.

The clay from our village and the ash from our hearth were our materials.

We were not interested in making work which left no trace of the potter. A perfect shape was of less interest to us than a form which carried the trace of our fingers. This year we have made over 100 pinch pots, so much so that our fingers work better if we are not watching the pot being shaped. The making of these small pots, usually mulled wine cups, is knowledge held in our hands and fingers rather than cognitive or aware knowledge. Our fingers sing the pots, imagine the pots. 

Ceramics then for us has developed as a way of finding place. It is about ourselves and our landscape and how the two exist side by side and within. It is about identity and imagination and a sense of self. And it feels completely natural, as if we have always known and seen the landscape in this way. And yet we know it is a new understanding.

The Australian poet Martin Harrison moved from Sydney to the country. In his essay ‘Country and how to get there’(2004:102) he writes of the way self and place can relate. “This moment of convergence, a moment where things at last fit appropriately into their environment, often occurs seamlessly and as if it has always been the way to name and see.”

Catching Harrison’s sentiments in our clay-hands we see our work in developing glazes as derived from, and reflecting the landscape. It has increased our understanding of our selves and our sense of place.

Clay

Clays are blends which can be adjusted to enhance their plasticity, shrinkage, reaction to firing, colour and compatibility to glaze and engobes.

According to Scott (1998: 25) clays are made up on four main ingredients- Clay, Flux, Filler and Opener.

Most commercially prepared clays provide information about firing temperature and are designed to minimize shrinkage and maximise compatibility with glazes. However all clays should be tested. 

Commercially Prepared Clay

Scott (1998: 22) when discussing plasticity and shrinkage of clays notes that water is always present in clay, even in dry clay and divides the water content into three main types.
Water of Plasticity is the water that surrounds the particles of clay allowing them to slide around each other. In green clay ready for working the water content is usually around 20% of the weight of the clay.
Pore Water can be up to 10% of the weight of the clay. It is the water which fills the spaces made from the irregular crystals of the clay particles. Apparently dry clay contains this trapped water. The clay needs to be heated to above 100degrees c in order to expel this water.
Chemically Combined Water. The actual chemical symbol for “pure” clay  is Alumina (Al), Silica (SiO) and water (H2O) Al2O3.2SiO2.2H2O. The water section is often left of the equation for ease as it does not play a part in ceramic fusion, but it is useful to remember that this chemically combined water takes a firing of 600degrees C to be expelled.

The water content contributes to clay shrinkage. Experiments to test the various shrinkage quality of clays were carried out on a variety of commercially prepared clays.

Clay Shrinkage

Various merits of the clay

Sculptural clay has the least shrinkage at both earthenware and stoneware firing. The small shrinkage at stoneware temperatures is significant. However it is the most strongly coloured of all the clays. This can be an advantage when fired at earthenware temperatures and the natural colour of the clay can enhance glazes and engobes. At other times when a white clay is needed the strong colour can be a disadvantage. 

TMK retained a whiteness which is also useful but it did not retain its flatness or shape.

The RGH kept its shape and its flatness well. In addition it fires at stoneware to a light grey colour which would respond well to certain engobe and glaze work.  
 

Local Clay

Wanting to experiment with the local materials we decided to dig and prepare local Clunes’ clay.

Clunes, an old gold mining town, is located in a minerally rich area. The local soil is thick, sticky, dark in colour. It is excellent for growing plants from autumn to spring but in summer cracks and dries out. Significantly the topsoil does not retain moisture well.

We first looked for clay deposits along the creek bed asking local fossickers and fishermen for suitable locations. This proved to be a fruitless perhaps because the locals did not want us disturbing their favourite fishing or fossicking places.

We then investigated an open cut hill at the back of the Clunes football oval.

It contained clays and ochres of different colours: reds, whites and yellows.

We dug this clay, shifted it, ground lumps with a mortar and pestle and collected buckets of a fine redish power which we then mixed with water to form a clay. It kept shape and was very moist.

We noted Daniel Rhode’s advice. “Adding the clay to the water, rather than the water to the clay, ensures that each particle of clay gets thoroughly wet and does not ball up into a sticky mass of partly wet, partly dry clay”  (1962:49) 

Making buttons from the different colours we fired the clay at stoneware temperature.

Button 1 – terracotta colour

Button 2 – white

Button 3 – darker red colour

Button 4 - yellow to ochre colour

The colour variation which was marked in the raw clay state was lost in the firing process.

Button 3 interested us the most. We liked both the colour and the way the button of clay kept its shape.

Experiments with using the clay

We tried putting the ball clay 20%-Clunesclay 80%  through an extruder but it broke up.
 
We tried making simple pinch pots with it and found it difficult to work with and very wet. Dryer versions were not as plastic.

We had a problem with the way the clay related to water. If we gave it enough to ensure it was plastic it proved difficult to shape. If we reduced the water it cracked and broke and lost plasticity.

We introduced ball clay to our local clay at various percentages. We needed to first test the clay in small amounts and in such a way as to not damage other experiments in the kiln so we made buttons of the new clay and placing it on prepared tiles for fire testing.

Apart from not adhering to the tiles, the clay, in all its forms behaved well indicating that additional experiments were productive.
 
 

 
We experimented by adding ball clay in amounts of 5%, 10% and 15%
The shrink test showed

Clunes Clay

As the ball clay is increased so too is the shrinkage.

What was notable was the way the clay kept flat and retained its flatness and shape.

At 20% we began working with the clay making a small pinch pot to experiment with the way the clay kept its shape in firing. 

The colour of the fired clay is a strong dark brown, reminiscent of raku clay. This is not surprising because of the large amount of iron in the clay.

Subsequently 3 larger pinch pots were made. They bisque fired well. They were glazes, as per our experiments with glazing see below, and placed in the wood fire kiln. 

We note from Bernard Leach how clays are improved by souring and kneading.
“Souring and kneading cause the flat particles of clay to lie close together and in more parallel directions, thus increasing the molecular attraction and therefore the plasticity.” (1965:48).

Rhodes stresses the advantages of keeping clay for a period of time because it  produces bacteria. “The bacteria produces acid residues and promotes the formation of gels.” (Rhodes 1962: 52) The working of  bacteria can be enhanced by adding some old clay to the new which speeds up the process.

To this end we made up two batches of clay 80% Clunes clay and 20% ball clay. To one we added a small quantity of raku, kneading it in. To the other we let it sit. These will be worked on next semester.

Our work with this clay is ongoing.

We realised then that mixed with other ingredients this clay could form the basis of some interesting glazes. See Glaze Section for this work.

Slips, Engobes and Opacifiers

Slips

We read up on slips and found Rhodes useful.  “Slips glazes are glazes which are made wholly or largely from clays of low fusion point….Since all clay which a low melting point contain iron and other mineral impurities, slip glazes have colour range limited to tan, browns, and black.” (Rhodes 1962:186)

Bernard Leach (1965:54) gives recipes for slips used at St Ives.

Leach slip
China clay 6
Ball clay 2
Feldspar 2
To these he adds oxides for colouring.

Slips for higher temperature have a limited colour range.

We experimented with made-up Lismore slips in brown, tan, white and blue, on our raku ware, on our large busts and on the maquettes.

Which was then dipped in Shina Shino glaze. This close up shows the double dipping forming the white glaze line over the tan and brown slips.

Blue, white and tan Lismore slips were used. We noted how the slips did not run in the firing process.

Below is a close up of the blue slip on raku clay with a Shina Shino glaze. The Shino glaze covered irregularly which is a feature of the final pot.

On another pot the tan slip was dipped in limestone glaze which created a contrast between the tan and white surfaces. 

Using slips as colour on busts

Because we were firing the busts at earthenware temperature we could experiment with coloured underglazes.

We decided to use commercially produced underglazes which have the advantage of uniformity of colour because they are ground finely and the composition remain consistent.

We combined blue, white, tan and black Lismore slips and a variety of commercially produced green underglaze pigments. The pigments were watered down slightly and applied with a brush. The slips were built up to give depth much as paint might be.

Before firing:

On firing we found that the colour of the pigments and slips were faithful and met our expectations.

After firing – a close up of the layering of slip colour to reveal a mask-like quality to the work.

In another work the sculptural clay was first covered with a layer of white Lismore slip which was used as an undercoat over the sculptural clay colour. The slip was applied in several coats. 

It was then painted with a variety of underglaze pigments which were mixed with white Lismore slip as a base. The various colours were applied with brushes.

The slips were then given a tin glaze which produced a Toby-jug look

Bringing the Slips Back to our Landscape

Feeling confident with slip application we experimented with using slips made of Clunes clay. We applied these to pots and platters.  Below is an example of a platter first painted with Clunes clay slip then given a redgum ash glaze and fired to cone 10 at reduction. The glaze was base 4A and 25% ash.

Engobes

Using the recipes in Rhodes (1962:161), repeated in Currie (1985:152), we mixed up engobes for greenware, (wet and dry) and bisque ware.
 

Experiments with wet clay are forthcoming. On bisque firing the colours were insipid but we need to wait until we see the results after firing at cone 10.

The dry greenware experiments can be seen below. Both examples have been bisqued and fired at cone 10.

These were tested on prepared raku clay tiles because we wanted to test the engobes ability to cover coloured clay. We found a good coverage on the raku clay.

We then added colour which also gave a strong coverage on coloured clay. This time we used sculptural clay.

We tested for a pallet of colours using oxides. From Rhodes we took the following formulae (Rhodes 1962:162)

Colouring Oxides in Engobes

The colour tests were carried out on test tiles by mixing 1% more colorant than given in the above table so as to achieve saturation to 100mils of uncoloured engobe. Then the colour was gradually diluted by adding one teaspoon of uncoloured engobe. This produced a run of up to 13 colours of decreasing intensity.

The engobes were bisque fired and then fired to cone 10.

Note: The experiments with green (4% copper oxide), purple brown (7% manganese dioxide) and yellow (7% yellow iron oxide) were not successful.  To achieve these colours further work is required.

Engobes and Glaze

We carried out a series of experiments using engobes with our glazes on platters of various sizes. We experience crawling of the shino and oil-like pooling of the ash.

The experiments were not successful and produced some of our most unpleasing results. The engobes we had made were not compatible with our ash glazes. To continue this work we needed to develop suitable glazes which would complement, aesthetically and chemically the engobes.

Wanting to continue our work on ash glazes we ceased working in this area.

Opacifiers

Rhodes (1962:123) points out that glazes can be opaque from many causes.
Causes:
            Underfiring of glazes
            Entrapped bubbles in the glaze
Specific mixture of glasses of different indexes of refraction
Development of crystals in the glaze as it cools
Increase of certain oxides beyond their normal limits

Opacity can be obtained by using oxides, as above.
Tin oxide gives a soft texture and enhances the colours of glazes. 1-3% produces semi opaqueness and cloudiness.
Zirconium oxide may be used instead of tin oxide. 7% will make most glazes opaque. 12% will produce white glazes.
Titanium dioxide will pick up colour, particularly iron producing creams instead of whites.
Mixing with a box-ash glaze we made a line blend of  0, 1, 3 and 5% oxide to glaze.

Opacifier on white clay

Even as little as 1% of the various oxides (see last row) produces a clouding of the glaze and adds considerably to its sense of depth. At 5% the tin oxide-glaze became solid and the titanium crawled. The best effects are between 1-3% oxide.

Opacifiers on sculptural clay

Here we wanted to test the effect of the opacifiers on clay with a additional iron.

The titanium oxide (middle glaze) absorbed more of the iron in the clay and coloured giving a milky-brown mottled effect. Once again the best effects were between 1-3% for all oxides.

Ash Glazes

We began by finding 6 base glazes which we found in Daly (1995:15). Of these we particularly liked his base stoneware glaze E

Base Glaze 1A

Nepheline syenite 60
Whiting 18
Talc 14
Kaolin 18

This became our Base Glaze 1A. It is a white mat glaze with attractive cracking in both reduction and oxidation firing at cone 10.

Another useful glaze was his base stoneware glaze D, which we refer in our records as base glaze 4A

Base Glaze 4A

Potash Feldspar 63
Whiting 6
Talc 10
Bone ash 6
Silica 10
Kaolin 5

We experimented using these and adding various colourants. These are recorded in our glaze records as experiments 6A-13A and will not be discussed here.

We then tested the various fluxes because we wanted to see why we liked one base glaze over another. We tested nepheline syenite, potash feldspar, Cornish stone, soda feldspar, spodumene.

This was fascinating and we found our preference was for nepheline syenite at this time. We particularly like the nature of its opacity and its cracking. We were interested to see that it was the main flux in the base glaze 1A which we also preferred. The flux then in its raw state, and in its glaze recipe, reacted in a way we found interesting. It became our preferred flux.

Additional uses of this flux can be seen in the section Experiments with natural materials, below.

Volumetric Blending - Biaxial Blends (Currie 1985:29) 

We carried out a volumetric blend to examine the differing effects of silica in relation to gradually differing amounts of feldspar, whiting and kaolin.

We did the .6 feldspar test using base glazes

The glazes were exactly mixed as per Currie.

The experiment was technically tricky to perform particularly getting enough of the glaze mixture on each part of the test tile and not let it overflow to the other section. It took us two attempts to succeed at this.

Currie (1986:61) wrote of the feldspar in this test being quite overpowering and of a matt pink effect on glazes 11 and 16.

We did not observe this effect possibly because of variations in the temperature on firing. What we did observe however was a tendency in glazes 2-13 to crawl. Glazes 21, 26, 31 had translucent qualities. The glazes 22, 27 and 32 were highly crazed.  Glaze 18 has a high sheen and on a curved or raised surface does not crackle.

Experiments with natural materials

We experimented with found materials and returned to our source of Clunes clay.

To the clay we added coffee grinds because with June running a B&B she had a large source of these.

We made a line test of coffee to Clunes clay -
20% coffee; 40% coffee; 50% coffee; 60% coffee to Clunes clay

The most successful result was the 20% coffee - 80% clay where the coffee integrated with the clay adding texture and colour.  In the other experiments there was too much coffee and it separated in firing.

We will continue our experiments using coffee and adding flux. In particular we will use Cornish stone because in our previous experiment with flux, (as above) we think its matt and speckled property will possibly be enhance by the coffee granules. 

It was of interest to us to hear a documentary about the work of ANU materials scientist Mr Tony Flynn who added coffee grounds to clay to form a primitive water filter. The clay could be fired at low temperatures, in for example a campfire using dried cow manure as fuel. Under these conditions the coffee grounds created minute holes in the clay which was then used successfully as a primitive water filter.  (Radio Australia Innovations 4 April 2005)

Ash experiments

We became fascinated with the possibilities of ash glazes.  For us the ash, particularly in combinations with our local clay, represented our landscape. For us, as noted by Elias (2005:6), ‘the Earth is origin’. Although we do not have the resources to be as exclusive as Steve Harrison (2004:30) who laments having to use 3% of bentonite mined not from his land, we sympathise with his attempts to create exclusively from the landscape. We engage with his concept of terroir.

Ash

Wood ash is made up of 10 to 15% alumina; 30-70% silica; up to 15% potash; up to 30% lime along with some iron oxide, phosphorus, magnesia and other elements depending on the source of the wood. (Rhodes 1962:188)

Wood varied not only over species but also over climatic conditions and is further effected by cultivation. This is discussed in detail in Phil Rogers’ seminal work on ash glazing. (Rogers 1991) He comments: “Ash glazes are the most complex of all. This was, he said, because in ashes we are dealing with nature’s mixture.” (Rogers 1991:23)

Our first experiments was to made a line blend of red gum ash and Clunes clay. The blend was from 100% ash to 100% clay in 10% intriguers. The firings were carried out in oxidization.

The most interesting glazes occurred at 60% ash and 70% ash.

We then tested these further on prepared rings and tiles. Making 60, 65 and 70 percent ash glazes.

The most successful 70% ash, 30% Clunes clay. It’s a golden honey colour which fills crevices well but which could cause some problem being so runny. It would need modification on anything but a flat tray- like surface.

We found that we needed to sieve the ash and clay mixture more thoroughly to reduce the foreign material from the clay which was not burning off in firing. This made us aware that we need to investigate further various treatments and washing of the ash before use. We note that Rogers has a section dealing with this.

Ash, clay and colour experiments

Revisiting the base glaze 1A and some of our earlier colour experiments we then decided to select the most successful experiments and try them in oxidation, reduction on white clay and on recycled clay. We wanted to see how the glazes worked over these variables in order to increase our understanding of the variables.

The tiles were fired in oxidation; the rings in reduction.

These experiments are recorded in our glaze book as glazes 7A; 11A and 14A-24A

From these we further developed 14A

Glaze 14A

Base glaze 1A
48 Red gum ash

In oxidation it creates a crystal-like surface in ambers to green. We tired it on a tray with indentations. We used recycle clay to increase the iron reaction. The glaze, dominantly green but ranges in colour to ambers. It is deep in the troughs of the tray and the crazing creates a crystal-like quality. It gives the effect of  water and ice. 

We also like the way Glaze 24 ran and the colours mixed forming a complexity. But they were very runny and needed to be further worked on a flat surface.

Glaze 24 A

Mixture of 11A and 17A double dipping

We made a tray of recycled clay to increase the iron reaction with the glaze and doubled dipped. The double glaze over the large surface has potential. We noted the glaze works better on curved surfaces and this is quite visible on the tray.

The problem now is the amount of glaze to use. In places the glaze is deep and mysterious, in other places the light blue takes over and the glaze is too thin.  We need to further work on this to create a glaze that more resembles the sea or sky at night - a mass of blues swirling on each other and moving to grey and black.

Glaze 21A

Base Glaze 4A
48 Red Gum ash
applied on Clunes Clay slip

We really liked the effect of this glaze in both oxidation and reduction.

To increase the effect of the glaze and the clay we decided to apply the glaze directly to a pinch pot made of Clunes clay and bisque fired.

The result pleased us. It is a complex glaze of creams to browns. It has a high sheen. The complexity and depth of the glaze as it reacted with the iron and other minerals in the clay creating patters and allowing the clay surface colours to at times come through - not unlike the effect of Shina Shino.

We further investigated the effects of clay and ash on larger surfaces. We choose a prepared sculptural clay tray. We mixed a glaze of 30% Clunes clay and 70% ash and fired it at cone 10 in reduction.

The ash has melted well and the colour of the clay has muted its colour creating layers of different hues of brown.

The glaze covered well but we could add even more to increase its complexity. This will form the basis of further experiments.

The Triaxial

We then carried out a triaxial blend of  red gum ash, Clunes clay and nepheline syenite. We followed the method set out in Currie (1985:87). We carried out this experiment on both white clay and recycled clay because we found that the ash reacts to the iron in the clay.

The experiment was fired in oxidation.

This is our most successful and interesting experiment so far.

There is a large variety between shiny, matt and crackled glazes in the blend.

Glaze 18, (30 flux and 20 clay) created a shiny red button suitable for use in decorative work. Where as glaze 17, (40 flux and 10 clay) gave a button of brown with red specks.

Glaze 12, (30 flux 10 clay, 10 ash) gives a matt finish with grey background and brown to black markings. There is a depth to this glaze. It is granite or rock-like.

Glaze7 and 11 (40 flux, 10 ash  & 30 flux and 20 ash) have similar characteristics. They are very crystal-like, so greatly crazed that they appear opaque. Glaze 7 is a yellow colour whereas glaze 11 is nearly clear.

Glaze 6 (30ash, 20 clay) is a matt finish, layers of texture and colour predominately a muddy brown with a lighter brown flex. This would be interesting to experiment on a larger surface. 

This experiment has provides us with a rich source for further investigation and a fascinating pallet. We now want to repeat this experiment using different fluxes and clays.

Ash Glaze Application Experiments

Developing the triaxal results we mixed a number of glazes using a combination of % ash to either base glaze 1A or base glaze 4A.

We applied these to 29 raku pinch pot cups.

The raku was Blackwattle Buff Raku ; Walkers Raku Gold; Keanu White Raku. We recorded what glazes we applied to each cup and the method of application.

These were then fired in the test kiln in two batches, one at cone 11 and the second firing at cone 9. Note the cone 11 firing included a soaking of 30 minutes.

Results

Several glazes ran and pooled in the cone 11 firing. There was a variety of colour and effects.

Green glazes

A shiny glaze with luminosity.
This green tinge was a combination of 4A and 70 ash. In this instance the glazes were applied simply.

Blue glaze

4A and 50 or 60 ash. This was enhanced with brown overtones where June’s glaze (12 triaxial) was flicked onto the glaze.

Pink glaze

Pink occurred when base glaze 1A combined with another glaze- ie T3 or T5 when the dominant glaze was the base1A glaze. This resulted in a variety of effect always mat, often crackled and with pink tones.

Forest effect

Base glaze 1A and T3 or T12 on light coloured clay produced a running effect like a forest – canopy or roots. They ran quite a lot and to achieve this effect wadding tiles need to be used. 

 Light flecks – cream-green

A very attractive lightly coloured  glaze. On light clay with Base glaze 4A and 60 ash. This was added to by a rim of 5T.

Note: 5T and 3T need to be used in moderation as an overuse produces a very ordinary brown glaze which appears underdeveloped.

W F effect

On a white raku pot with a dark raku foot Base Glaze 1A and 4T. The base glaze was applied and the 4T splashed on its side. There was crackling and a translucent blue in certain lights.

Note on a pot which used this combination but put the 4T in the bottom of the cup the results were far less satisfactory.  

Lismore Slip

Lismore slip is made of:
Ball Clay 15
Kaolin 20
Silica 20
Talc 20

and is coloured by adding

For Tan
6% Red Iron

For Blue
2% Cobalt Carb
2% Red Iron

For Black
20% Red Iron Oxide
2%Cobalt Oxide
8% Manganese Dioxide

Applied on the outside of the pot in dot splashes. The slip remained as splashed - no running at all. For this use it was not satisfactory but elsewhere might create an interesting effect.

T12- June’s Glaze

Our first named glaze. At high temperature because of the amount of feldspar (30%) it is a stable glaze, consistent at high temperatures and has an effective stony look. Dark brown with lighter flecks. At the lower temperature of cone 9 it was underdeveloped and an ordinary brown colour, not achieving its full potential.

White stoneware pot

Clayworks TMK clay. The outside was T3 and T12, the kiln was soaked and reached cone 11. The white stoneware turned a terracotta reddish colour, probably a soaking of the iron in the Clunes clay in T3 and T12  

Experiments on larger shapes- trays

We discovered that the first question to address with ash glazes and trays is the amount of ash and the nature of the ridges for the ash to fall into.

Best effects were obtained with the rolling-pin ridges- deep ridges in one direction.

Also it is better to not completely cover the tray with glaze, leaving the clay to engage and come through the glaze.

Darker clays produced a better effect.

On second firing we had failure and the complexity became muddled. We began a collection of failed trays.

We experimented with applying the ash directly onto greenware but found that the trays broke and cracked – the amount of ash and moister were too great.

Also we found that mixing box and redgum ash was unsuccessful particularly over trays which previously had been engobed and Shaner Shino (see below) glazed. The combination produced a dark engine oil effect.

Shaner Shino was developed by the US potter David Shaner:
Soda Feldspar 10.8
Spodumene 15.2
Kaolin 10.0
Soda Ash 4.0
Nepheline Syenite 45.0
Ball Clay 15

One tray was effective, best on darker clay. It was a combination of Base 4A and 24 ash over a slip of Clunes clay.

This was fired in a wood firing and also in a reduction normal firing.

The glaze was consistent both times.  

 Glaze on darker clay

Ash with Silica and Soda Potash

We made a triaxial of both redgum and box ash with silica and soda feldspar. There were two big additions to our pallet. In the box ash we found a light to quite azure blue occurring in T 9, 10 and 15. In the redgum triaxial we achieved red coppery colours. These occured in T 14 and 15. We decided to carry out further work with these glazes.

We then made quads using Clunes clay, redgum, dolomite and nepheline syenite and another using box ash. We fired these on both white and recycled clay but the results were not productive and we didn’t take the quads any further.

We isolated out 6 glazes from this work.

We then mixed up the glazes, sieved them and tested them on open pinch pots with a base of 1A and 4A.  Unfortunately the sieving through the finest sieves removed much of the colour and produced a watered down effect. To the left is the redish effect of  14 Red gum triaxial on a base of 1A glaze. In the photo below, to the right is the soft blue of the box gum, 10 box gum triaxial on 1A glaze.

We then decided to not use such a fine sieve opting for either no sieving or a courser mesh.  We also wanted to test the effects of the glaze running and so experimented on both beakers and trays.

We made a number of wadding tiles to assist in the firing.
Wadding: 60% calcined Alumina, 40% ball clay.

Conclusion

After attending John Eagles workshop we are keen to experiment with our ash glazes but using thinner layers and building up complexity with different combinations.

We also want to experiment with different clays especially raku clays- this builds on our mulled wine cups.

We feel as if we have just scratched the surface of ash glazes.

Firing

Test Kiln – Reduction

Achieved cone 9
3/8/05

Achieved cone 10
12/10/05

Achieved cone 11
27/7/05

7 cubic foot kiln

This kiln is naturally a reduction kiln and if the flue is closed over carbon builds up. To check this take plug out- if built up with carbon open flue.

However there are times when a little carbon is required and this tendency of the kiln can be played with.

31/8/05

Soot Free Firing
12/10/05

Pit Firing

In our reading of the journals we noted the sense of place is an important part of the work of many Australian ceramic artists. In particular we saw how Anita McIntyre’s work is described by Haynes (2005: 17) as “highly evocative of a particular place”, and later in the same article as “the intimacy of the individual’s experience of the landscape.”  Further, Reece in his article appropriately titled Essence of Place (2005:75) writes of his own work “I am liberating and at the same time exposing the nature of soul of the ‘rock’.”

In order to further investigate our sense of place we organised a local pit firing to be held in conjunction with the CFA’s bonfire night.

Clunes Pit Firing 30/10/05                  

The Clunes pit-firing was quite an event and generated interest among local artists and residents as well.  A pit about 2 metres long by 60cm. in depth and a little over a metre wide was dug out close to the very large bonfire.  The proximity to the large fire was an advantage as the fire acted as a giant windbreak sheltering the pots in the pit.

The pots were laid on top of hardwood sawdust and then covered with pinecones and shredded paper.  Branches with dried twig material were laid on top of the pinecones.  The fire was lit  around 7PM and  when everything was well ablaze,  small branches continued to be  placed on the pit at regular intervals for about 30 minutes.

The fire was very hot and the estimate of the temperature was somewhere between 900-1000 degrees.  Some time later the pit was covered with a heavy mesh and tin was placed over the whole area to keep in the heat.  The bonfire kept blazing overnight.

Next morning at 10.30.AM  we inspected the pit.  There had been no damage during the night from falling debris, or animals. The ash and coals in the pit were still very hot so we decided to leave inspecting the pots further until later in the afternoon, giving larger pots time to cool further before removal.

At 4PM (using industrial quality gloves) we started removing the pots from the kiln.  To our delight only three of the forty pots fired incurred any damage. The bonfire had successfully kept the wind from cooling the pit and damaging large numbers of pots.  One larger pot which had an effective finish from the firing unfortunately sustained a small crack.

The results of the firing were pleasing. With the experience gained from this firing we will modify the materials, and the way in which they were used so that there is a greater range of colour on the pots in a future pit firing.  Pinecones hold heat so they are obviously a good choice of combustible material.

This event has been an excellent way to inform the community of  another aspect of  visual arts that until this time they had little knowledge or experience.  Most people present were keen to find out how many pots survived the firing.

Lehman (in Ceramic Monthly 2001:ix-x) reflects: “It dawned on me that these pots, fired with this fuel, were perhaps more mine than any others I would ever make: precisely because of the Chinese elm. These trees had patiently, over a series of decades, grown on my land, absorbed the nutrients and solubles from my soil, been subject to the seasons of my climate. Then in the journey of the firing, these trees had given back to my pots the very solubles they had taken from my soil.”

Bibliography

Ceramics Monthly, Wood Firing, Journeys and Techniques: A Collection of Articles from Ceramics Monthly with a Foreword by Dick Lehman, The  American Ceramics Society, Ohio, 2001

Currie, Ian Stoneware Glazes: A systematic approach Bootstrap Press, Maryvale Qld, 1985

Daly, Greg Glazes and Glazing Techniques: A glaze journey Kangaroo Press, Kenthurst NSW, 1995

Elias, Ann ‘Across the Generations’ The Journal of Australian Ceramics, July 2005 Pp6-7

Harrison, Martin ‘Country and how to get there’ in Who Wants To Create Australia Halstead, Sydney, 2004 Pp100-107

Harrison, Steve ‘From the Ground Up’ in The Journal of Australian Ceramics November 2004 P30-31

Haynes, Peter ‘Anita McIntyre- Recent Works’ in The Journal of Australian Ceramics, April 2005, Pp16-18

Leach, Bernard A Potter’s Book Faber & Faber, London, 1965

Radio Australia Innovations  4 April 2005 http//www.abc.net.au/ra/innovations/stories/s1339270.htm cited 18/6/05

Reece, Simon ‘Essence of Place” in The Journal of Australian Ceramics, April 2005 Pp 74-78

Rhodes, Daniel Clay and Glazes for the Potter Chilton, Philadelphia, 1962

Rogers, Phil Ash Glazes A&C Black, London, 1991

Sanders, Herbert H Glazes for Special Effects, Watson-Guptill, New York, 1974

Scott, David Clays and Glazes in Studio Ceramics, Crowood Press, Wiltshire, 1998
Sutherland, Brian Glazes from Natural Sources: A Working Handbook for Potters, Batsford, London 1987

Tichane, Robert Ash Glaze, New York State Institute for Glaze Research, New York, 1987

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