Oxides stains: Cathy Keys reports on her research aimed at extending a palette of ceramic oxide colour finishes.
WHEN INTRODUCED TO handbuilding ceramic forms using the coiling technique I was instructed in smoothing back and joining individual coils to ensure the cohesion and physical strength of a form. For me the resulting textural beauty of a handbuilt coiling technique was lost as soon as the wet coils were flattened. I found the smooth surface left me with a sort of 'grief' for the line work of the coil. Digging around in this quite emotional response to clay I have spent the past few years experimenting to create a fired surface that retains the visual integrity of each piece of clay used in construction. Clays with a high grog content are best suited to my handbuilding technique, the strength of the piece being generated by the way coils are woven together while respecting the compression and tension forces in a finished piece. The coiling process and the forms and textures it creates are inspired by observing the interaction of climatic and environmental phenomenon in Australia and are linked to a broader concern with landscapes and concepts of place and identity.
Keeping to this conceptual framework and coil aesthetic I moved away from applying glazes to the fired work which tended to shroud or flatten the surface. (This surface is made up of layers of coils between 5 and 10 mm in width and the average 'valley' produced when these coils meet is probably around 3 mm deep.) Instead I focused on the application of basic oxides as a stain to the bisqued work. Initially I rubbed a red iron oxide stain straight into the skin of single fired work finishing the surface with a ceramic sealant. I experimented with alternative clay bodies and different firing temperatures to obtain a colour range of browns and dark rusty reds. I did not mix the oxide with anything other than water at a 10 per cent concentration (that is 10g of oxide to 100 ml of water). The colour was drawn into the 'valleys' and when the oxide residue was wiped off the 'ridges' of each coil. I then progressed to using a second firing at either earthenware or stoneware temperatures depending on the clay body used, which exposed the earthy qualities of the clay and left a matt finish to the stained line work. Seeking a black stain I tested copper oxide and manganese oxide at a range of concentrations preferring to work with the greeny/black of fired black copper oxide--again finding the best results around a 10 per cent concentration in water.
After some success exhibiting and selling my work the temptation was to maintain my limited palette of finishes and spend all available time on the evolving forms. However, as my subject matter expanded I began to feel restrained by the colour range of rusty browns and black. After experiencing high losses and being quite fearless through the research and development of a coil construction technique it was now time to take some risks on the actually colouring and finishing of my sculptures. With funding from the Australian Government through the Australia Council and a Creative Sparks Grant from the Brisbane City Council and Queensland Government, through Arts Queensland I began a series of experiments using an accurate set of weight scales and a range of oxides. These oxides included: chromium oxide, copper oxide, cobalt oxide, ilmenite, iron oxide, manganese dioxide, nickel oxide, rutile, tin oxide and vandium pentoxide.
I researched the use of oxides as ceramic colourants taking careful note of recommended concentrations and as a result decided to introduce into the tests a range of commercially produced powdered ceramic body stains and underglaze stains to ensure the broadest possible colour spectrum. I numbered and bisqued just under 500 hand-coiled test tiles using a range of commercially available grogged and fine clays suitable for earthenware, stoneware and porcelain firings. I designed four different line blend experiments (one for earthenware and three for stoneware firings) on two or more different clay bodies. I performed each line blend test using 10 different oxides or commercial stains with varying concentrations (between 0.5 per cent and 10 per cent), each mixed in 100 ml of water; this generated 55 combinations per line blend test. I brushed on each blend and then rubbed back the surface to leave the pigmentation in the 'valleys' of each test tile. I fired all in the same commercial electric kilns in oxidation firing then mounted the results on eight large boards.
The tests with oxides or commercial body stains and underglaze stains by themselves after an oxidation firing showed similar results to those reported by others. For example greens were achieved with chrome and copper oxides, blues with cobalt oxides, browns and rusty reds with iron oxides, browns and tans with manganese, nickel and rutile, blacks with saturated copper and manganese oxides and yellows with vanadium pentoxide. Commercial stains provided purer and brighter colours but lacked the range of textural finishes displayed by the oxides.
One of the four line blend tests used commercial stains and oxides and was designed to produced a broad range of colours. The earthenware tests on a white grogged clay resulted in colours that seemed too pastel or watery for my current work. When the same line blend was used on a grogged clay that fired to a biscuit/pink at earthenware temperatures, the clay body overwhelmed and 'pinked' all the colours. Another of the line blends was designed with oxides at high concentration (10 per cent) for use on clay that would vitrify at stoneware temperatures. These oxide concentrations were too strong and there was little colour range but a wide variation of dirty browns, ink blues and blacks. At stoneware temperature on a white clay I found a great dark green as a result of combining copper oxide (2 per cent) and chromium oxide (5 per cent); a rich orange/yellow using citrus underglaze stain (10 per cent) and rutile (3 per cent); and a lively teale using chromium oxide (5 per cent) and dark blue underglaze stain (10 per cent).
Initially I was disappointed with the results, for when I analysed the eight board of 55 tiles each, I found I was only really interested in the colour results of three to five tiles. It was in the process of exploring why I was rejecting test tiles that it I made significant discoveries. Once I began to look past just the resulting colour range and see the minute and subtle differences between finishes the results of the experiments were rewarding.
In the act of choosing one colour blend test tile over another I was becoming more conscious of the finish I was seeking (or not seeking) and this had as much to do with the texture of a ceramic colour in its fired form between the coils as it did the colour. Often it wasn't the colour of the tile that was drawing my attention at all, but the way the stain 'grabbed' or ran up the valley between coils. For example, colour blends containing nickel oxide resulted in a hue that seemed to creep up over the ridge of each coil gradually intensifying in colour in the valley. This was in contrast to most other blends which showed a definite line or 'high tide' marks at the point at which the stain had been wiped off the ridge of the coil. It also became clear that one of the reasons I was rejecting many of the earthenware tiles was because some of these colour blends had left a pale 'high tide' mark a millimetre above the more intense colour of the 'low tide' mark in the bottom of the valley. This secondary 'tide' line weakened the overall visual effect even from some distance away.
I began questioning myself, and taking notes on, what I considered beautiful, ugly or indifferent to my tastes. What results assisted in developing an aesthetic language so important to expressing the conceptual ideas underpinning my current and future work? For example, I knew I liked a matt colour finish and on sculptural pieces concerned with the dryness of drought was appropriate. I had already begun experimenting in distressing and cracking individual coils in response to the drought but what if the actual colour stain was 'parched' as was sometimes achieved with blends containing heavy concentrations of iron oxide? Conversely, for pieces concerned with conceptually 'holding' water there was something alluring in the 'wetness' resulting from some of the blends containing copper oxide and manganese dioxide because of their shiny metallic finish. This was especially pronounced in clays that had vitrified.
Care in wiping back the colour blends on bisqued work was important to the fired finish. This was especially the case for colour blends containing cobalt oxide because it is so intense and while most other stains did not leave trace marks as a result of the wiping back process, cobalt did. Even colour blends with low concentrations of cobalt left 'grubby' wipe marks across the ridges of coils, especially tiles where the clay had vitrified. The colour and texture of the fired clay became important. The two grogged clays used and fired to stoneware temperatures created a more subtle shift from ridge with no colour, to valley with intense colour, because the raised grog did not take the stain and through tiny shadows visually softened the transition.
The process of such extensive testing and analysing has made me far more conscious of my own 'aesthetic language'. Being selective and continuing to observe these test tiles, I am currently honing in on a weathered, aged and parched finish to my ceramic work which for now means use of a dry or matt texture in the valleys of my coil work. Sculptures drawn from earthy land-based themes and environments are working best with rich browns and olive colours--of which I now have an extensive selection.
The process has not only extended my colour palette but triggered a line of inquiring into a whole new range of textures and finishes for future work. I am now designing work through drawings and sketches with my line blend boards beside me and researching the addition of other glaze materials to exaggerate and enhance the finished textures of oxides and stains. I intend researching simple blends with varying concentrations of two or three oxides and stains to find the right intensity of colour and fit with whatever my chosen clay body is. But the biggest and most exciting leap has been that these oxide stains have opened my imagination to a whole range of other possibilities in terms of the forms and ideas I can express in my work.
I am a Brisbane based ceramist, with a background education in architecture. I create coiled handbuilt sculptural forms. This article is concerned with reporting on some research I completed aimed at extending a palette of ceramic oxide colour finishes. Thinking the experiments and associated analysis would have technical outcomes focused on resulting colours I have been quite surprised to discover that the most significant findings were instead linked to a more conscious understanding of my personal design and aesthetic goals; that through the testing of a wider range of oxides and ceramic stains in a more controlled and documented process I have moved closer to discovering and articulating my own visual language.
It seemed that the best results were from the line blends fired to stoneware temperatures using low concentrations of oxides (0.5-5 per cent) and relatively high concentrations of commercial stains (10 per cent). These tests resulted in a broad range of colours. Closer inspection revealed a softening or deepening of the commercial stain colours when oxides were added.
Oxide blends that 'bite' into the clay body are important to my current work. In fact there is so much in these eight boards of test tiles that it may take a lifetime to work through them.
This project has been assisted by the Australian Government, through the Australia Council, its arts funding and advisory body. The project was also assisted by a Creative Sparks Grant from the Brisbane City Council and the Queensland Government, through Arts Queensland.
1. Berensohn, Paulus. Finding One's Way with Clay: pinched pottery and the color of clay, Simon and Schuster, New York. 1980.
2. Connell, Jo, 2003, The Potter's Guide to Ceramic Surfaces, New Burlington Books, London.
3. Memmott, Harry, The Australian Pottery Book, Paul Hamlyn, Sydney. 1970.
4. Murfitt, Stephen, 2002, The Glaze Book: A Visual Catalogue of Decorative Ceramic Glazes, Thames and Hudson, London.
5. Peterson, Susan, and Peterson, Jan, The Craft and Art of Clay, Laurance King Publishing, London. 2003.
6. Warshaw, Josie, The Complete Practical Potter, Lorenz Books, New York. 1999.
Cathy Keys is a ceramist with a background education in architecture from Brisbane, Australia.
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|Date:||Jul 1, 2007|
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