I am a week into my month long residency at Guldagergaard International Ceramic Research Centre in Skaelskor, Denmark. There are several artists in residence here and new potters coming every week to attend workshops and wood firings.
I have been trying out a variety of grogged and flecked stoneware clays and making test pieces to fire next week in a wood kiln. I am using an Australian Venco wheel with a wireless Bluetooth pedal. The studio space is very well equipped with a glaze room, drying cupboard, mould making and slipcasting rooms as well as electric kilns.
I have also taught a special effect glazes workshop where we made a range of lichen, lava, oilspot, crackle, gloop and metallic glazes.
Thank you to the Making Waves Trust for providing me with a grant.
Studio potters often worry about the large amount of energy they need to fire kilns to a high enough temperature to produce their ware. In addition, the materials they use, clays and glaze ingredients, are dug from the earth and are not renewable. However, with the exception of pure, white kaolin, clay is very common worldwide, the result of weathering and crumbling of mountains, the sticky residue deposited in rivers and lakes over millions of years, part of the geological cycle which could be seen as long term, natural recycling.
Many glaze materials are also common, including quartz, limestone, feldspar and iron oxide, a colourant that has been used since the earliest pottery. However, some of the colouring oxides including cobalt are rare, expensive and difficult to mine and occur in areas of the world where unethical practices take place.
It is really important to learn as much as you can about your materials, where they come from, how they are mined, what they are composed of and what each material is used for; clay, flux, glass former, stiffener, opacifier or colourant. When recycling ceramics, the clay and glaze waste need to be separated. If this is not done, the fluxes in the glaze may cause the recycled clay to warp and slump during firing.
Fortunately, there are several things we can do to make our pottery studio practices greener. Studio potters only use only a fraction of the materials and energy used by the ceramics industry, but together we can try to change the ways things are done and make our voices heard. I wrote a list for the Crafts Council of eight ways to make your studio pottery greener.
‘Climate change and air pollution are two of the biggest challenges facing the world today.’
Michael Lewis, E.ON UK Chief Executive
1. Use a green energy provider generating power from the sun, wind or water. Green energy can be used to fire electric kilns. For wood firing, make sure you use wood from a sustainable source or offcuts from woodworkers. To make firing economic, make sure the kiln is packed as full as possible every time you fire and consider reducing firing temperatures or firing times. Avoid breathing firing fumes by firing at night and ventilating the studio well.
2. Recycle all unfired clay. Collect together failed pots, throwing slurry, trimmings and turnings. If they are still in the wet state, wedge them together by combining into a large mass, cutting in half and slamming the two halves together repeatedly. If the clay has gone beyond leather hard, dry out until completely bone dry and then add to water to allow to slake down, leave to settle, then pour off excess water and dry out the slurry on a plaster batt to a workable consistency. Wedge and knead well before using.
3. Collect all clay washed down the sink in a settling tank, then recycle the slurry. Keep a separate bucket of water in the glazing area in which to wash hands, brushes, sieves and glazing tools, leave to settle overnight, pour off the water, then collect the settled glaze at the bottom and re-use. If you don’t separate the clay and glaze in this way, you will end up with a mixture of clay and glaze in the settling tank, which is more difficult to recycle.
4. Recycle excess glaze. Either wax the bottoms of pots to avoid glaze sticking, or scrape off glaze from the base using an old credit card, collect the scrapings and when you have enough, add to water and sieve. Overspray glaze from spray booths can also be collected. You will need to keep each glaze separate. Alternatively, you can collect all glaze scrapings together into one bucket, sieve and use as an ever evolvingmystery glaze, or add iron oxide to make a more consistent black glaze. If you must throw away glaze, leave to dry out and dispose of the solids in landfill, not down the drain.
5. Avoid using toxic glaze materials, including lead, barium carbonate (use strontium carbonate instead), chromium oxide and nickel oxide. Black clays often contain manganese dioxide and you should avoid breathing in the dust or firing fumes from this. Ask your supplier whether your cobalt comes from an ethically mined source and if not, consider using other colouring oxides instead. Iron oxide is the most widely available and non-toxic colouring oxide and gives colours from amber, through rust red to black.
Richenda Macgregor and Mel Chambers of Studio45 in Dartington, Devon advise
‘We only used non-toxic glazes at Studio 45 and ensured the firings were done at night to avoid any fumes in the studio during the day whilst people were present. The main thing was the large extractor fan built into the wall to draw out any fumes but as I say it wouldn’t have contaminated anything as they were non-toxic.
My best advice is to research non-toxic glazes and stick to those then everyone is happy.’
6. Save shards from broken pots and give to a mosaic artist or use as crocks for drainage at the bottom of flower pots. It is possible to recycle broken ceramics to make new glazes if you have access to a ball mill to grind them up small enough. In order to recycle fired pots, you need to divide the ceramics into unglazed or biscuit ware for use as grog in clay bodies and glazed ware and glass for re-use in glazes. Granby Workshops in Liverpool are one studio using 100% recycled ceramics from the pottery industry for their tableware.
7. Use waste materials such as wood ash from your wood burner or fireplace. This can be soaked in water, sieved then made into a glaze together with clay and feldspar. Wood ash acts as a flux and adds subtle colours from olive to bottle green. Other waste materials include ground sea shells and dust from quarries or marble workshops, all used as glaze fluxes. You can use small quantities of local clays as decorating slips and mixed into clay bodies, but if you want to dig larger amounts, you need to ask permission from the landowner.
8. Instead of firing in a gas kiln, you can achieve similar reduction glazes in an electric kiln by adding a reduction agent such as fine mesh silicon carbide to the glaze and an oxidising agent such as zinc oxide to mop up the excess carbon (you only need around 1% of the total dry glaze weight of each material). The silicon carbide breaks down above 1000°C into silicon and carbon and reacts with the oxygen in the glaze, changing the colours of iron oxide from amber yellow to celadon green and copper oxide from green to copper red. It is possible to achieve several classical Oriental glazes by this means, including Chun blue and celadon. You can find silicon carbide glaze recipes on glaze database glazy.org
In September I exhibited at the London Design Fair in the British Craft Pavilion curated by Hole and Corner magazine. Before the show, photographer Chloe Winstanley visited my studio in West London and took some lovely photos for an interview feature. At the show I met some other lovely potters, including Rebecca Proctor of Modern Craft Workshop in Cornwall, Matt and Catherine of Pottery West in Sheffield, Ana of Kana London and David Worsley of Dove Street Pottery in West Yorkshire. The look in the British Craft Pavilion was modern rustic, with modern furniture and textiles, hand-turned wooden bowls, forged steel knives, cast concrete and jesmonite, a material made from gypsum and acrylic resin. I also met Ali from Francli craftwear, who recently made me a split-leg pottery apron.
The show was very busy and I met many journalists, bloggers, curators, interior designers, restaurateurs and buyers as well as many old and new friends. Interiors journalist Barbara Chandler took a lovely photo and I shared the tube journey back home from East London with her. My stand was in a great location next to the cafe, talks and demonstration area, and a highlight was taking part in a chocolate tasting workshop with Land chocolate. I now have some new orders, commissions from restaurants and new ideas for upcoming glaze articles and books.
During our summer holiday in Cornwall we had a lovely walk along the SW coast path from Perranporth to Portreath, passing several abandoned mines and spoil heaps, great places to look for rocks and minerals.
We started our 12 mile walk at Perranporth, south of Newquay on the north Cornwall coast. At Cligga Head, we passed an abandoned tungsten mine, where they mined wolframite, a black mineral containing tungsten, iron and manganese. There was also a lot of greisen, decomposed granite, on the first step towards becoming china clay. While the granite mass was solidifying 300 million years ago, hot gases caused it to decompose. It is now easily weathered by the rain and sea and we could see white granules of quartz everywhere under the heather. The hot gases forced the granite up through cracks in the older Devonian slate rocks and caused minerals to dissolve and reform in seams. The ends of mine shafts can be seen in the cliff face, which is stained red with iron oxide.
Rocks and pebbles found on our walk. Bottom right, altered granite; the large white crystals are feldspar. Bottom left, turquoise rock stained with copper. Middle left, red rock stained with iron oxide. The black rocks and pebbles are Devonian slate (400 million years old), with white veins of quartz running through them.
At St Agnes head, there is a granite outcrop which has been weathered into a clay and sand deposit where clay is dug for the Leach Pottery. Further along the coast path is the remains of an old tin mine, Wheal Coates, where the chimney of the Victorian pump engine house still stands at the top of the cliffs. Tin ore was found in seams below sea level, and so water had to be pumped from the mine shafts. We tried throwing a rock down one of the old mine shafts and it took a very long time to hit the bottom.
We also had a lovely visit to the Leach Pottery in St Ives, where we were shown round the working studio by trainee potter Lexie Macleod. The potters use a mix of St. Agnes clay, ball clay from Devon and iron oxide to give the dark, toasted colour they want. They use several glazes, a green ash glaze, black tenmoku, a dolomite white and a white/orange shino. They often throw a hundred mugs in a day, which then take several more days to finish and add handles. Their outlets include Seasalt, who fund an apprentice, and David Mellor in London and Sheffield.
I am excited that my next book Science for Potters is coming out soon. The cover shows a pair of Atomic Bottles by Kate Malone, covered with atoms and crystals. The book will cover chemistry, geology, clay, crystals, the science behind colour and glazes. For anyone who would like to know a bit more about the science of pottery.
Clay is an amazing material. You can shape it and it holds its form, then you can fire it and it turns into stone. Under the microscope, clay is made up of tiny stacked hexagonal crystals, which are able to slide over each other when lubricated by water. The kaolinite image below is reproduced from the Images of clay archive of the Mineralogical Society of Great Britain & Ireland and The Clay Minerals Society.
Each clay crystal is made up of thousands of layers of silica tetrahedra and alumina octahedra. These can build up in alternating layers as in kaolin, or in three layers; silica-alumina-silica, as in bentonite. Water can get between the crystals, which enables them to slide easily over each other, allowing the clay to be moulded into shape. Kaolin is less plastic than bentonite as it has a larger particle size. A third type of clay, illite, is derived from mica, and is a constituent of red earthenware clays.
I often receive emails asking about glaze problems. It seems that students on ceramics degree courses are not taught very much about science or understanding the materials, but concentrate more on learning about art and design ideas and philosophy.
In Chemistry at school, I loved the periodic table. It neatly groups the elements so that each column contains elements with similar properties which react chemically in the same way, with metals on the left and centre and non-metals on the far right. The periodic table here shows the elements found in clays and glazes. The blank spaces are elements of less interest to potters. You can find the complete periodic table here.
I have been writing a book on Science for Potters for the American Ceramic Society. Several chapters are being published in Ceramics Monthly. You can read the full article on Chemistry for Potters here Bloomfield_Feb16
Originally published in February 2016 issue of Ceramics Monthly, p60-64. http://www.ceramicsmonthly.org . Copyright, The American Ceramic Society. Reprinted with permission.
Last week artist Sophie Glover came to my studio. She is making a large series of drawings of people working in their studios. She is really good at telling a story, showing multiple stages in the making process and picking out interesting details. I love the illustration of the wedging process and the wobbly bowl being thrown in the front centre of the drawing.
Sophie studied drawing at Falmouth University. She went to St James School in London, where her younger sister Amy was in the same class as my daughter Alice. Last year Sophie had a residency on an island near Finland, where she drew rocks and experimented with clay. She is using drawing not just as illustration, but as an art form in its own right. She is planning to make a large number of drawings of studios which you can see on her website www.sophieglover.co.uk.
It has been ten years since my first collaboration with Ruth Cross, who designed cosies to fit my porcelain mugs and teapots back in 2006. Since then, we have sold hundreds of cosy mugs and cosy teapots, featured in the press and been copied widely. Our cosy tea sets have sold in London, New York and Tokyo,
Since the Great Pottery Throw Down aired on BBC2, pottery and knitting have become the latest trend, although we dislike the homespun, not-just-for-grandmothers angle on crafts taken by many journalists and presenters such as Kirstie Allsopp.
Ruth has since written a book The Knitted Home and, as well as knitting, also turns her hand to making bespoke shoes with her husband Adam Law. If you feel inspired to knit a mug cosy, the pattern is now available online.