Linda Bloomfield

Kiln packed for the glaze firing

Ash glazes. I often make up a 100g glaze test and then try adding materials to improve it. In this series I started with 50:50 wood ash and potash feldspar, with 0.5% aluminium metal powder for reduction in an electric kiln, first tile, then 4% zinc oxide to oxidise any unused aluminium. These were both very runny so I added 20g ball clay in the third tile plus 5g China clay in the fourth tile. This glaze is matt and still runny so my next step will be to add 10g quartz to make it more glossy. I like ash glazes that are slightly runny and glossy where they pool.

Fifty pouring bowls and a few cups drying in the studio

Glaze tests, from left, transparent with added Thames mud, green wood ash glaze, shino over red iron oxide, all fired in an electric kiln

In London the summer has come at last. The summer solstice is one of my favourite times of year. I love the long hours of daylight, the meadows and wildflowers, the dappled light through the green leaves, the swallows and swifts in the skies.

Fresh Air Sculpture is an exhibition in a beautiful garden in the Cotswolds until 7th July. There are over 100 artists taking part.

My lichen inspired pieces make tangible the effects of air pollution on lichen biodiversity. At one end, the pieces are covered in lichen-effect glazes. At the other end of the series, there are only a dark and a white crawl glaze representing urban lichens and finally they become completely dark and barren.

Photo courtesy of and

Lovely to see my work in other people’s homes. Thank you for sending the photo

Open studios in Chiswick and Hammersmith start tomorrow evening, 14 June, 6-9pm then on Saturday and Sunday 15-16 June 11-6pm.

Looking forward to seeing some of you there. You can download the studio guide and map from artistsathome.co.uk

There are lots of other lovely artists and potters nearby: .stentzel

Delicious 30th wedding anniversary dinner with

Beautiful handmade pottery by of Whitstable.

Oysters, cured trout, crab, brill, wildflower panna cotta, chocolate macarons and mint tea.

Pots in the kiln. Not long until my open studio next weekend

Next weekend 14-16 June is my open studio, part of in Chiswick and Hammersmith. There are lots of other lovely artists and potters to see nearby. You are welcome to come and visit.

Friday 14 June 6-9pm, Saturday and Sunday 15-16 June 11am - 6pm. Nearest tube Stamford Brook. You can download a studio guide and map from artistsathome.co.uk

Testing an ash glaze fired in an electric kiln. I’m using aluminium metal powder as a reduction agent and zinc oxide in the glaze to clear up the unused aluminium, which leaves black specks in the glaze. The green colour is a good indication that the reduction worked. The iron in the wood ash would be yellow brown in oxidation. However, there are still some black specks left in the glaze. It’s also slightly too runny.

Firing in an electric kiln using green energy has a lower carbon footprint than using a gas or wood kiln.

Various colouring oxides in a strontium crater glaze. From top left base glaze, iron, cobalt, copper, nickel, vanadium and iron. It’s not as bright as the version using barium carbonate.

Back in the studio glazing today

Thank you for all your comments on my last few posts. Sustainability in ceramics is an interesting subject. Some think that process emissions from firing carbonates and high-carbon clays are insignificant, but that’s because they are comparing them to fossil fuels. Coal, oil and gas give off such a HUGE amount of carbon dioxide (and air pollution) that we have changed the entire world’s climate in only 150 years.

In comparison, yes, firing carbonates such as whiting and dolomite does give off a relatively small amount of carbon dioxide, but it’s not insignificant and it’s good to know about it.

This is a graph from The European Ceramic Industry Association’s Roadmap to 2050, published in 2020, aiming to be carbon neutral in just 26 years from now. This may be an impossible dream but it’s a good target to aim for.
https://www.ceramica.info/cerinfo-content/uploads/2021/12/ceramic-roadmap-to-2050-continuing-our-path-towards-climate-neutrality_LOW.pdf

The graph shows carbon dioxide emissions in the European ceramics industries from burning fuel for firing (blue), indirectly from electricity (orange) and process emissions from firing carbonates and high-carbon clays (grey). Fuel burning is by far the biggest contributor, with process emissions only a a fifth of this. By 2030, we hope electricity in Europe will be mostly green. By 2050, the ceramics industries in Europe hope to stop burning fossil fuels to fire ceramics. At that point, the process emissions will be the only carbon dioxide emissions left to worry about.

So I do think it’s worth thinking about them now, and thinking more generally about what we can do to make our practices more sustainable. What do you think?

What can potters do to reduce their carbon dioxide emissions?

This is a wood ash glaze, made from wood ash and feldspar (you could also add clay), with a tiny bit of aluminium powder for reduction, fired in an electric kiln using a green energy provider.

Wood ash is high in calcium, already comes in powder form and is easier to process than seashells or egg shells. Wood ash also contains other flux oxides needed to make a glaze: potassium, magnesium and silica. It makes a runny glaze all by itself. Burning wood does release carbon dioxide and can cause air pollution, but could be seen as part of the natural carbon cycle (the tree would have rotted and eventually released its carbon over time). This is better than mining and transporting 100 million year old chalk and releasing its carbon dioxide by firing it (similar to burning 300 million year old fossil fuels).

It’s good to use waste materials such as wood ash, and locally found materials such as clay from a building site or river bank. It’s also a good idea to recycle and reuse your own clay and waste glaze and use recycled packing materials (thank you to my family who are always giving me boxes).

Shipping is also a large part of our carbon footprint. I’m lucky to live in London with many of my clients nearby. I once even delivered some work across London by bicycle. What we really need is a green shipping company. Does anyone know of one ?

The carbon dioxide emissions from firing carbonates and carbon-rich clays are called Process emissions. In the cement/concrete industry they account for 65% of the emissions (the rest comes from fuel combustion for firing and electricity). In the ceramics industry (including brick and tile), they account for up to 30% of emissions, so are smaller but not insignificant.

So what can we do to avoid firing carbonates such as whiting and dolomite? We could replace them with silicates. Wollastonite is calcium silicate and supplies both calcium and silica to the glaze. You would need to reformulate the glaze on Glazy.org and remove some of the quartz or flint from your recipe to get the same chemical formula as the original glaze.

But unfortunately it’s not that simple. In the UK we have plentiful chalk and limestone but not wollastonite, so that has to be shipped from Finland, causing more carbon emissions and a price increase; wollastonite is almost double the price of whiting in the UK. So you would increase your carbon footprint by switching from whiting to wollastonite. If you live near a wollastonite mine, as in eastern USA and Canada, it would be a good idea to use that. You can tell by looking at the prices, if wollastonite is cheap, then it hasn’t been shipped far. If whiting is cheaper, then use that.

In the case of dolomite, you can use talc instead. Dolomite is made of calcium magnesium carbonate, while talc is magnesium silicate, so you would have to reformulate the glaze by adding calcium and reducing the silica in the glaze. Talc comes from France, so not too far to ship to the UK. However, there have been some issues with talc sources recently and it is also found in mines together with asbestos, so always wear a respirator when using it in the powdered form.

As for the other carbonates, there is not a good alternative for barium or strontium carbonate, as the sulphates give off toxic sulphur dioxide during firing.

Instead of lithium carbonate, you could use spodumene, but you would need five times as much. Owing to the price increase of lithium, it might be better to leave it out or substitute another flux such as zinc oxide.

This is clunch, a mixture of chalk and clay, on Salisbury Plain in Wiltshire, and Black Ven, the Blue Lias limestone and shale/clay cliff in Lyme Regis where Mary Anning found her fossils.

Chalk and limestone both contain calcium carbonate, used to make concrete and also in ceramic glazes. When you fire calcium carbonate to high temperatures, it gives off carbon dioxide gas, the cause of global warming. The cement/concrete industry is a huge contributor to carbon dioxide emissions but it has just struck me that we are doing the same when we use whiting in our glazes in ceramics, though on a much smaller scale.

Whiting, chalk, or calcium carbonate is a cheap, useful flux in glazes. It makes the glaze chemically stable and durable. Usually it contributes around a fifth of the glaze by weight. But whiting is not the only carbonate we use in glazes. Other carbonates include dolomite, magnesium carbonate, barium carbonate, strontium carbonate, lithium carbonate and soda ash. There are also carbonate forms of the colouring oxides: copper carbonate, cobalt carbonate, manganese carbonate and nickel carbonate. We only use these in small amounts but they do contribute to carbon emissions. I probably get through around 20kg of whiting a year, which produces 8.8kg carbon dioxide, which is small compared to the total carbon footprint of each mug (around 2kg) but worth thinking about.

I feel so lucky to be able to meet such lovely potters on my travels teaching glaze workshops. Thank you for inviting me. Here are just a few of them.

Looking forward to teaching at and soon.

Amazing ammonite fossils at Monmouth Beach, Lyme Regis. The last photo of the pavement outside the Lyme museum is Coade stone, stoneware replicas made using a clay body made from ball clay, flint and frit.

Yesterday was biodiversity day. I’m looking forward to in the Cotswolds, opening on 16th June. It’s a beautiful garden full of sculptures, including lichen inspired pieces by me and

Lichens are clean air indicators. The greater the biodiversity of lichens, the cleaner the air. They are the early warning signal that we need to clean up emissions from industry, agriculture, traffic and wood burning.

Pots in the studio, matt glazes

Lichen effect glazes on recycled porcelain

More bowls in strontium turquoise and jugs in satin matt white

Strontium blue glaze over crater slip

Strontium matt blue bowl

Thank you and nick_grellier for including my work in this new book and also for the happy coincidence of it being shown together with the work of cousin

The work in the book by 99 artists responding to a call on social media by exploring how creativity can act as a coping strategy was also shown in an exhibition last May

Pots from the Wall of Women
Ann Stokes
Lucie Rie
Katherine Pleydell Bouverie
Sandy Brown

We went to see A Yorkshire Tea Ceremony, the collection of Bill Ismay at the Centre of Ceramic Art curated by Helen Walsh. The teapot by Geoffrey Whiting was used by Bill Ismay every day and the caddy still contained traces of Lapsang Souchong.

Lucie Rie was not satisfied with the glaze on the blue vase which Ismay bought, so she made him another one, which she thought had a more successful glaze. In the second one, the blue comes through only in the indentations and the granular manganese in the clay body has flowed to make brown streaks.

There was a modelled blue tit by Rosemary Wren, pots by Elizabeth Fritsch and a yellow lidded canister by

We really enjoyed seeing Ismay’s collection of functional pots; mugs, jugs, teapots, vases, and reading the stories behind them.

We also saw mugs and plates by in the gallery shop.

Crawl glazes made on my glaze workshop at . There are two main types, one using zinc oxide (first image) and the other using light magnesium carbonate (second and third images). Glazes that are high in kaolin such as shino can also crawl. Another type of crawl glaze uses bone ash but I can never get these to work.

These materials all absorb a lot of water and when it evaporates, the drying glaze shrinks and cracks. These cracks widen during the firing to leave small islands of glaze with bare clay in between, an effect that resembles lichen. With enough flux and heat, the islands can turn into beads of glaze.

Interesting to compare lava glazes using strontium (first image) and barium (second image). Copper oxide is turquoise in the barium glaze and green in the strontium glaze. Cobalt oxide is a stronger, brighter blue in the barium glaze, while in the strontium glaze the lighter blue has a green layer underneath. Cobalt can turn green in high alumina glazes like this. The recipe is similar to .pinnell ‘s strontium crater glaze but with less strontium.

The craters come from 2% silicon carbide and 2% titanium dioxide which combine to make carbon dioxide gas during the firing. The glaze needs to be high in alumina to make it viscous enough to trap the bubbles of gas without healing over.

The main advantage of using strontium carbonate is that it is not toxic, unlike barium carbonate.