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.
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.
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.
Pyrometric cones on broken kiln shelf ready for the kiln
The temperature gauges
Firing temperature schedule
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.
Bricks in place at entrance
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!
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.
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.
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.
This afternoon I’ve been making press moulded shapes ready to start sticking them together tomorrow to build large lattice structures.
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…
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.
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.
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.
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
(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.
Renata 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
In my tutorial with David last week we discussed colour theory and the way putting colour on the back of flat planes can reflect the light in a halo of that colour around the edges. As an example he suggested I look at the first year fine art project displayed on the third floor – I hadn’t looked closely enough at these to notice the optical effect before but it makes the images pop. I glued some coloured paper to the back of my cardboard cutouts and the result above shows a very subtle halo of green and red light shining behind them. It reminds me of the hazy reflection of light you get on overcast days like the ones we had at Port Eynon. If I manage to make some of these in porcelain paper clay I could glaze the backs to get a similar effect.
After Laura’s plaster casting workshop I was keen to try printing onto plaster because I hadn’t tried it before and I saw the opportunity to make more slab-like forms which I could assemble as a kind of theatrical scenery. I rolled coils of clay and pressed these onto an inked up plate, creating walls around different sections. Next I poured in plaster to a thickness of about 1cm and reinforced the back with scrim. I mixed up two lots of 2 pints water/plaster so I didn’t have to do the whole plate at once. I should have been much neater with the clay by cutting walls from a slab because I would have had to file down the edges less this way. The resulting sections are a bit too thick – maybe I could have poured the plaster sooner. On the plus side, lots of detail came out from the intaglio plate.
I then set these upright in a bed if plaster (4 pints) which again, was poured a bit late so looks like icing slapped onto a cake with a palette knife. The scene looks a bit naff and reminds me more of a snowscene with ice and glaciers than a beach. I like the idea of placing a second inked up plate onto the drying plaster then hanging up the sections when they’re dry so the print is shown on both sides.
I also tried using coloured slips and sgarffito on slabs of clay. Inspired by Morgan’s Vicarious Wednesday talk I tried using paper resist stencils but discovered I have very little patience when it comes to decorating. Hopefully the slabs below will fire black and white.
I’ve also been working on making paperclay for the first time. Porcelain casting slip can’t be used for this purpose so instead I had to use porcelain from a bag. I dried out the clay then ground it to a powder in a pestle and mortar, added water, then let it slake down overnight. In the morning I poured off excess water and soaked the paper pulp (ratio of 1:3 to the clay) for 2 hours before sieving it (60 mesh) to get rid of excess water. I mixed the paper and slip together by hand but the consistency was very lumpy so Matt showed me how to use the glaze mixer which blends the paper pulp into a smooth consistency.
I made up an ink with black underglaze, a small amount of borax frit to make it less powdery (about 5% is ideal) and copperplate oil. The powders were sieved through 200 mesh then the oil was added gradually, applied to the plate and rubbed off with scrim the same as with the intaglio ink. This afternoon I built a wall around the plate and poured in the porcelain paperclay slip with the hope it will be dry by tomorrow with the ink printed on. The underglaze should stay on when fired but it will need a transparent glaze to seal it. I’m worried the clay might not dry in time for tomorrow’s assessment so I may try using a heatgun to speed up the process.