Glaze Research

20190513_124438 (626x800)While testing for suitable glazes for my sculptural vessels I came across a few exciting results, not really suitable for my pieces but interesting nonetheless. The two reduction fired glazes on the left here were supposed to be matte pink (coloured by rutile) but have instead turned pale turquoise which is not what I intended. The bottom right one however is a beautiful dry lavender colour and although I found the colour too bright and poppy to tie in with my theme of rethinking the country potter’s place in society, it could look great on sculptural pieces and reminds me of barium glazes. The dry purple effect is cause by a mixture of spodumene, talc, cobalt carb, silica and kaolin.20190513_124510 (800x327)

Since I couldn’t fire my vessels with the terracotta extrusions in the reduction kiln I tested a few oxidation glazes to try and get some subtle, satin or matte results that might echo the subtle ash glazes of Katherine Pleydell-Bouverie. Trying to multitask and confusing my glazes, I ended up firing these above to 1280C instead of 1220C so that rather than matte pinks and yellows I got some unattractive and super glossy results. The high iron content of the reduction st Thomas clay may have also altered the results.

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I kept getting glazes designed to be matte or satin coming out super glossy which would detract from the forms themselves and hide the traces and marks in the clay. The satin gloss blue (top right, above) surprised me with its depth and intensity. It’s such a uniform, bold, unsubtle shade of blue, reminding me of children’s toys and lego blocks, I struggle to think of it looking great on any piece of ceramics. One of my favourites above is the shino on top of tenmoku (second from left at a bottom row) which has a metallic lichen-like black smudging over the dark brown surface and shimmers without being overly reflective.

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Surprisingly I thought the glazes turned out much more effective on top of high fired terracotta – the shiny pink glaze shows speckling of tiny metallic crystals and the blues have much more depth and variation where they break to dark on the edges.

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The pieces that didn’t make it to the exhibition



New Glazes for Fractured Vessels


After my previous blog post about the kinds of surfaces I want on my sculptural vessels I created a series of glaze tests. Realising that I wouldn’t be able to fire my terracotta vessels or those with terracotta extrusions in the reduction kiln because of the risk of the clay melting or becoming too brittle, I decided to test some in the oxidation test kilns too. Above are my results from the gas kiln which all give a bright but slightly earthy dry surface that I thought would be less distracting than the shiny surfaces of my previous vessels.

The oxidation glazes (above) turned out a lot more glossy and gaudy than I expected. I’ve turned instead this week to the dry glazes book for simple recipes, quick to mix because of a small number of ingredients. Yixia suggested I use ordinary stoneware glazes but fire them to a lower temperature so they don’t mature completely and remain dry and pastel coloured like she has been doing. It was interesting speaking to Hannah too who has been using ferric oxide raku glazing. For her the firing process is the most important part and she decides on her forms based on how to show these firing effects best. For myself it’s the other way around, starting with form and thinking which surface will work best afterwards. I think most makers prioritise either the form or the surface.

The large glazed vessel forms shown here were all fired in the large red gas kiln, the first time I’ve fired work in this kiln since starting university. While the top half reached 1280C, unfortunately the cone at the bottom looks to have only reached about 1220/1240C. Perhaps as a result of this, on the largest of my thrown and altered constructions the glaze flakes off and hasn’t fused to the clay body. The glaze on the sculpture above is the same speckled blue-green that you can see on the first test piece at the top of the page, but because of the nature of the firing has instead become a very fluid dinosaur green, too variegated in shades to work well with the complex forms. It’s a set-back as it was one of my favourite shapes and as I don’t have time for in-depth glaze refining in these last few weeks, I’m going to abandon this glaze completely for the time being.

The photos above show two pieces almost completed and with surfaces I would be happy to show in my degree show. The sculptural jar was made in the spirit of some of the vessels I saw in Sandy Brown’s studio – bottomless because there is no concern with function here. Like her vessels which were often just canvases, not designed to hold anything except for surface decoration. I like to think of mine as sketches of pots in three-dimension. They look like pots and reference traditional vessel forms but are completely impractical and stitched together, optical illusions that subvert our expectation. The mustard yellow glaze works very well and gives a buttery texture that’s not too shiny to distract from the form. Iron oxide in the glaze gives it this colour but I wonder if I substituted that for cobalt, rutile or manganese, could I create similarly textured glazes in different colours?

L6 Term 1 Technical Project: Reduction Glazes

Images and Key in the link:
Technical Project PDF

I began this term with the intention of developing a series of ash glazes with the hope of getting similarly expressive effects to those in the wood kiln at HDK. The project would also link in with my growing interest in ‘non-spaces’ through using plants from hedgerows and Cardiff’s invisible edgelands. Looking at the ash glazes of Bernard Leach and Katherine Pleydell Bouverie, I admired the quiet, subtle colours and how they work in a calming way on the viewer. Over the summer I collected together a few different ashes – from our log burning fireplace at home as well as from bracken and rushes I had sourced in the countryside in North Wales. I dry sieved these ashes without washing as I had read in the Phil Rogers glaze book that it wasn’t necessary to wash ashes.

Using the simple 60:40 ash to feldspar ratio recommended by Phil Rogers, I experimented with different feldspars, discovering that Potash crazed the most. I also discovered that increasing the proportion of China Clay made the glaze more matte (Test No1.1). Unfortunately the glaze application on the test tiles is patchy since the tiny amounts of ash I had to work with meant the mixtures ended up containing too much water. I left them to evaporate overnight but the small amount of ash meant I couldn’t get a very thick coverage. A second series of line blends (Test No1.2) was made to see what happened when I added increasing amounts of Potash Feldspar to different ashes. Ideally I would have added increasing amounts of ash instead since these results are too similar. The problems I had with obtaining enough ash led me to work with different glazes instead. All my ash tests were fired in reduction although I did test them in Oxidation too but they were colourless.

I liked one of my ash glaze tests very much because of its matte quality, strong iron speckling and mint green colour (Ash glaze A6 on the PDF) so as result decided to experiment with creating glazes that had a similar quality of subtlety and softness. I came across a glaze I had adapted from Jeremy Jernegan’s dry glaze handbook last year. The original glaze had been a matte white reduction glaze with Potash feldspar being the main ingredient. I had adapted the feldspars (as I did with the ash glazes) and discovered that adding Nepheline Syenite instead created a shiner, more viscous glaze (probably because it is higher in alumina than Potash). As I hoped to use these glazes on functional jars and bowls I didn’t want them to be too matte and flaky.

The original glaze is white however with Nepheline Syenite it becomes blue-white with patches of pink flushing depending on the reduction and application. I wanted a series of glazes with a similar satin quality but in different colours so added metal colourants to the base recipe in proportions as shown in the PDF (Test No2.1) and then, deciding these were too dark, created a Triaxial Blend with the Grey-blue, Turquoise and the lighter base glaze. I added 4 brushed on layers to each of the 16 tiles but unfortunately the results are a lot drier than I expected, not really suitable for functional vessels. The darkness of the glazes is probably a result of using Reduction St Thomas which is a darker clay body than the usual white St Thomas, which I chose because of the iron spotting it encourages. The dryness of the glazes in this test could be a result of them being on the lower level of the gas kiln where they perhaps didn’t quite all reach vitrification temperature.

Having never done a glaze technical before I felt a bit lost as to where to begin and how to alter glazes to get the results I wanted. Although the idea of using natural materials seemed attractive as it fitted with my philosophies of material vitality, finding the materials is such a dedication that it didn’t seem to be practical with the large quantities of glaze I needed for my functional vessels.  This project has been valuable to explore how colourants can impact glazes though and made me confident using the reduction kiln which I used for the first time this term.


First Reduction Firing

Last Friday I fired the little yellow gas kiln at CSAD for my first time. Starting from about 8.40am the kiln climbed fast to begin with (up to 220C by 9am) and then rose steadily by about 100C per hour, a little slower than in previous weeks because of fluctuations in gas pressure (probably because gas was being used in the foundry). At 1000C, just before 1pm, the flue at the top back of the kiln was covered over in order to create a reduction atmosphere and was left this way for most of the final part of firing. As you can see in the image below two large pyrometric 1280 (09) cones were placed in the spyholes in the front top and back. By 3pm the top cone had completely melted while the bottom one was still only bending a little so in order to reach an even kiln temperature Gemma opened up the flue at the back which had been covered for reduction, encouraging air flow in the kiln. The firing was finished by 3.20pm.
In order to get a better impression of how the gas kiln behaves it could be an idea to place cones at the back on the right side too to see if there are hotter or cooler spots. Since the pyrometer was placed in the right side of the kiln and only read 1237C when the top cone was gone, it suggests to me that the right side might be a little cooler. It might also be valuable to place a 1300C cone at the top too to get a more accurate reading.

I was a little disappointed upon opening the kiln on Sunday since lots of the glazes hadn’t behaved as I hoped, although there were a handful of beautiful bowls and jars – my own nephyline syenite matte pink glaze worked particularly well. The main problem was that lots of the glazes were applied too thinly. My glaze application has improved since first year when I was painting them on and had lots of patchy results. Now I make a big enough batch of glaze to dip the pots in and this results in a much more even coverage. The chun and celadon which I had tested in Sweden turned out ugly patchy browns but perhaps they were just not thick enough. The best pieces seemed to be the ones most enclosed in the centre of the kiln shelves. More reduction could have been encouraged by packing the kiln tighter or even putting work in saggars. The insides of the lidded jars had a lot more brighter colours than the outsides because they’d reduced better.

While I only used one layer of glaze on the vessels, I tried layering different glazes on the test tiles above and the results turned out to be a lot more exciting this way. The shino over matte pink results in a matte lavender while the pink over chun creates a purple/blue crystalline – like glaze breaking to pale yellow where thin. The pastel colours in blues, greens, pinks and lavender have a quality of delicacy, lightness and quietness much like the glazes of Katherine Pleydell-Bouvarie. I’m drawn much more to the matter surfaces and they way they soak up the light in a soft, introverted manner. Somehow these surfaces feel more organic than the glistening, glassy ones which have an almost sticky, plastic texture. Shinyness distracts from the form too.  My next step will be to experiment with overlaying these glazes on vessels in a gas firing hopefully later this week.

Anagama Firing Day 1 & 2: Packing

Over the past couple of days a group of us current ceramics students at HDK along with some alumni, have come together to pack the 3.5m square anagama kiln at Nääs along with our smaller wood firing kiln ‘Elinor’. We’ll begin firing early Monday morning, working in shifts of four hours per pair until Wednesday night when the anagama reaches about 1300C. Elinor can be fired to temperature in one day so on the Monday we’ll be feeding two kilns simultaneously.

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My vessels for the firing glazed in shino, chun and green celadon

We began by emptying all our boxes and unwrapping our glazed pots. The anagama needed to be swept out before the kiln could be packed and wadding had to be prepared. The recipes for wadding vary but we used approximately 7 parts Alumina to 3 parts Kaolin (China clay) alongside rye, water and a generous shake of sawdust. This makes up a kind of off-white putty which is rolled into small cocktail sausage shapes that stick all the kiln shelves and supports together. Since the anagama slopes inside, the supports don’t lie flat but are angled on the base and need to be stuck down. Small balls of wadding are spat on and stuck to the base of pots before they’re placed in the kiln. It can be knocked off after the firing but without it the coating of ash through the kiln could stick everything together.

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Unpacked and laid out ready to fire

The chun type glazes were placed closer to the back of the kiln because they’re liable to run while glazes that required higher temperatures to melt were put close to the opening where the flame can hit them. Unbisqued work was also put to the back to avoid cracking. This is one of the differences between an anagama and an ordinary wood kiln – in a wood kiln the pots are shielded from the flames while in an anagama they are exposed to them. The temperature is also encouraged to fluctuate in this firing e.g after 1260C we will drop down to 1220, then up to 1270, down to 1240 and so forth to climb steadily, building up lots of layers of ash. We’ll have a pyrometer in the kiln but have also placed eight lots of seven pyrometric cones ranging from 1000C to 1325C in order to measure the temperature difference throughout. These cones are visible in the peep holes down either side of the anagama’s length.

Today we also prepared the daub to seal in the bricks at the kiln’s entrance – 50/50 sand and clay which could be dug up just a few meters away from the kiln, with added water to make a paste. A space for the firebox was kept at the front – here we can push in wood to feed the fire. The base of the entrance is built with alternating columns of soft and hard bricks so that the soft ones can be removed if needed to take out fuel from inside. Around the door too are hard bricks as supports. Some of the bricks at the front had to be sawed and sanded down to make them fit as tightly together as possible.

When packing it’s important to think of how the flames will flow. Like water they will always take the easiest route so it’s good to have a range of heights on each shelf and nothing too large close to the back which could block off flames to the smaller pots in the narrower end. Since we didn’t have quite enough work to fill Elinor, soft bricks were places in the gaps which will keep the air flowing evenly throughout. Generally the packing hasn’t been an especially difficult process, it just takes a lot of time and shuffling things around. Fingers crossed for the next step!


Firing Fail

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I felt my heart sink when I went to open the kiln this morning. Instead of a rainbow of bright colours – lime greens, turquoises, salmon pinks and cobalt blue, I found my series of white earthenware thrown plates had all turned a yellowish off-white. Checking back over the glazes I’d used I realised I’d made some mistakes with the calculations when I tried to double the ingredients. I’d added 1% of coloured stain to the new glazes instead of 10% to the base glaze. 

I should have realised something was off by the pale colour of the glazes in liquid form. I was hoping to display these colour experiments on the wall for next week’s corridor exhibition but I’ll have to think of something else instead. The firing itself didn’t really go to plan either. The first time I though I’d put the kiln on, I came back in the morning to find the kiln still on 50C. I hadn’t pressed and held the start button down to begin the program!

Hopefully I’ve learnt a lesson to keep neater notebooks so I’m not cramming illegible glaze recipes into every area of free blank space.

Press Moulding

Last week I tried to make my own press mould for the first time, not very successfully. My plan is to create press moulds from composite thrown forms so I can build them together into large sculptures. I find it easier to hand build on a large scale with grogged clay, but it’s painful and not very effective to throw with heavily grogged clay, so I will create press moulds of the thrown objects instead. These forms will be for my final individual project . I’ve narrowed the brief down to explore the imagery of in Italo Calvino’s ‘Invisible Cities’, Ch. Thin Cities 3, especially the idea of a network of pipes as underground veins…

“Whether Armilla is like this because it is unfinished or because it has been demolished, whether the cause is some enchantment or only a whim, I do not know. The fact remains that it has no walls, no ceilings, no floors: it has nothing that makes it seem a city except the water pipes that rise vertically where the houses should be and spread out horizontally where the floors should be: a forest of pipes that end in taps, showers, spouts, overflows. “

I began by bisque firing a form I’d constructed from thrown sections then made a two piece plaster mould of this. The ceramic got stuck in the plaster when I tried to release it, either because I hadn’t used enough soft soap or because I hadn’t placed the middle line in the exact centre.

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Since for press moulding it doesn’t matter that the plaster is completely sealed together (unlike slip casting), I used glue to stick the broken plaster pieces together.

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This afternoon I’ve been making press moulded shapes ready to start sticking them together tomorrow to build large lattice structures.

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Alongside these I’ve been throwing functional ware for the anagama firing we’ll do at Naas in a couple of weeks. These 500g bowls are a little on the heavy side, I’m still a little afraid I’ll turn off too much clay and end up with a hole. I’m been experimenting with the angle and depth of the footrings to see what looks best…

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Room/Space Project Development

20180312_151307 (600x800)With two weeks left to go of the Room project I think it’s time for reflection on how the project has developed so far and how I intend to bring my exploration of ideas to culminate in a final installation.

I chose the HDK’s black grogged stoneware clay to begin making with, the graininess makes it ideal to hand build with because it keeps its form well. At first I worked quite strictly from the collages I made from the earlier tram drawings but discovered quickly that this ‘steampunk’ aesthetic wasn’t what I wanted. I don’t like the way the clay is manipulated to look like metal or rivets, instead of celebrating the qualities of this material I am hiding it. I realise that since this bothers me perhaps the tenet of ‘truth to material’ is somewhat important in my work.

After a tutorial and discussing with others I decided to focus on simplified forms instead of details. I still preferred my collages to the clay models, so this week I took the approach of collaging clay to create more two-dimensional ‘illustrations’ of my illustrations. These were made by rolling thin slabs and assembling them roughly and quickly together when in a leather hard state. The rough edges and unfinished, breaking apart look is an attempt to capture the fuzziness of how the memory of a place appears in our mind.

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In a group tutorial today a few people commented on the fresh and spontaneous way these objects feel because they have been constructed quickly and fairly sloppily. Although I would like to see the sculptures on a bigger scale it would be hard to get the same effect of haziness and sketchiness.  20180321_131528 (800x400)Looking for a semi-matte base glaze with which to experiment I found this simple recipe online at

Satin Base Glaze Cone 4 (1168C)
Frit                  50                    (used Borax)
Kaolin             20
Dolomite        30

I added 10% coloured stains in different proportions of colour to this to try and match the colours found in tram interiors in Gothenburg. The orange, yellow and light blue are prefect although the pink was supposed to be red and the blue is too purple. Unfortunately on the black stoneware these glazes bubble but I still intend to use these glazes to decorate my original ‘sketches’ in clay – the haziness of the colour might work to reflect the blurriness of memory and the patchiness might reference the dirtiness of the trams.

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Over the next two weeks I’m going to continue working with this collage technique but in a white low firing clay, hopeful the juxtaposition of these ‘sketched’ sculptures and a smooth, uniform and neatly coloured glaze will create impact. I’m going to try working on a slightly bigger scale so that there is some different in height levels in the final staircase exhibition. I have tried placing some objects on the stairs already to see how they look in this different context but the dark colour of the clay means they are lost against the surroundings. I hope the bright colours will change this and create a sense of playfulness and intrigue. I also plan to create more accurate blue and red glazes, a grey and a lemon yellow. 

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A Gothenburg tram interior :

Celadon Mugs

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I wanted food-safe glazes to decorate a series of white stoneware mugs I made last month and decided to use a celadon base glaze then adjust the percentages of iron oxide and tin oxide to get a line blend. Celadons originated in Japan and the jade colour is caused by iron oxide being starved of oxygen in a reduction atmosphere during firing.

The original A60 base celadon glaze (1) uses the recipe below. It fits the body well and is a grey-turquoise satin colour.
CORNISH STONE              56
BALL CLAY                        20
WOLLASTONITE              20
TALK                                  3.5
(RED IRON OXIDE             1.5)

(2)  1.5 IRON OX. & 1 TIN OX.
I thought the addition of tin would make the glaze more matte, but the effect here is the opposite, the colour becomes thinner, more watery. Brown speckles.

(3) 2 IRON OX.
My favourite mug, the addition of 0.5g more Iron ox. to the original recipe gives a slightly darker more yellow-green than blue-green.

(4) 3 IRON OX.
With double the iron oxide in the original recipe, the glaze becomes less smooth and the surface begins to break apart a little. This is a much darker, more ‘forest’ green than the others, breaking to dark brown where thin.

(5) 1.5 IRON OX. & 2 TIN OX.
Again the addition of tin has made the glaze less transparent but the speckling is attractive. Bluer.

(6) 2 IRON OX & 2 TIN OX.
Strangely, despite being the most different mixture to the original recipe, this one looks most similar to (1). The more iron in proportion to tin, the fewer speckles.

Birthday Glaze

20180209_161019 (600x800).jpgRenata held a fun glaze workshop with us in which we made a glaze based on our date of birth. We randomly chose glaze materials to mix in proportion to the year, month and day we were born. By comparing each other’s glazes we could get a good idea of how each material behaves when fired.

My glaze was the result of mixing a high proportion of whiting with some dolomite and ball clay and a small amount of Wood ash. Fired to stoneware temperature the result is a very dry, matte  and slightly flaky off -white/pale green glaze blending into pink lower down in a gradient effect. The ash has pooled in a shiny green line along the base where it has melted. It’s not suitable for functional ware because it hasn’t fully melted, but I’m excited to use it to decorate sculptural forms.

Whiting (calcium carbonate) acts as a flux and also creates matte effects (as does dolomite). Ball clay is a source of alumina and enhances glaze suspension. I want to make a series of glaze tests using the same four ingredients but changing their percentages so that I can get a better glaze fit.

UPDATE: After a couple of months the glaze has flaked off completely