Kiln Building with Joe Finch

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DAY 1

I spent the weekend at the home of jeweller and ceramic artist Linda Unsworth (Pampeliska) in the Preselli hills where a group of us had got together under the leadership of potter and expert kiln builder Joe Finch to build Linda a small wood kiln in the garden.

We began with a flat concrete base into which holes had been drilled to let the moisture escape. It’s also possible to build onto a base of hollow concrete blocks with insluating blanket over the top. Firebricks had been laid out on top of the concrete in the shape of the kiln’s base and we built up onto this one layer at a time, photographing each layer. On the outer brick layer were light insulating bricks and heavier firebricks on the inside wall against where the flames will be. The chimney was built in a more aesthetic red reclaimed firebrick.

Joe’s kiln design is five bricks across and four wide and he’d built a model from Lego to guide us. Joe advises working out the size of the kiln you want after deciding how many kiln shelves you want to fit inside. The two chambers either side are fireboxes into which the wood will be fed through two openings at the front creating a ‘fast fire’ down draft style of kiln – the chamber in the middle will pull the flames back down and out the chimney. You can see in the photo that the second layer of bricks is pushed out slightly in the firebox to create a ledge. This is for the perforated brick layer to sit on. The idea is that the embers from the logs burning on the firebars above will drop down onto these and the oxygen through the holes will help combust them, meaning you don’t have to rake out the embers so often like in other kilns. In the chimney you can see a space where the bricks are missing – this is where the damper will be placed and bricks can be pulled out here to create reduction.

As the kiln got taller we added the firebars – hollow tubes of refractory fireclay onto which the logs will be placed. These need to be loose enough so they can be pulled out and replaced if needed. We continued to build up the bricks layer by layer, insulating on the outside and firebricks on the inside, sometimes having to saw bricks in half to fill in cracks and filling smaller gaps with gaskets of insulating ceramic fibre. Things became more complicated when we began the kiln chamber floor. We placed the flattest kiln shelves we could find on top of the fireboxes, leaving two gaps for the back for the flames to flow through and one at the front in the middle. We covered the flue to the chimney too.

Things picked up after this stage when the job got easier – we simply built the insulating bricks up in layers around the perimeter of the kiln chamber. Once the desired height was reached (about 2m high for the entire kiln) Linda painted numbers on the bricks that will make up the door using watered down red iron oxide. Joe then sawed out the door.

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DAY 2

We began Sunday morning by mixing up a mortar for the reclaimed molar bricks for the outside kiln cladding. This second layer of insulating bricks isn’t necessary but makes the kiln look more aesthetic. As a cheaper alternative it’s possible to cover the inner layer of bricks in insulating fibre then add a corrugated iron shell.

The mortar was a mixture of ball clay, sand, water and red iron oxide (the iron colours the mixture pink so it blends in better with the red bricks). The bricks were each soaked in water for a few seconds before building with so they absorbed the mortar better. Since the bricks were reclaimed we spent some time scraping the layer of old mortar off the surfaces before we could begin the next stage.

The cone spyholes in the back had to be adjusted for this second layer of bricks so we made new longer ones which can be pushed in at an angle. After completing one wall of outer layer we added the supporting angle irons on the outer corners and secured these together with a 12mm threaded rod (could use 5mm), then slid in horizontal ones between them.

The roof was constructed with three layers of insulating bricks cut at angles to make an arch. A D shaped wooden arc support frame was held up by planks underneath and we built the arches over the top, supported either side by bricks cut in half length-ways. Once the other outer walls have been completed the frame should be able to drop and slide out through the kiln entrance leaving a freestanding roof. Unfortunately by the end of the weekend we’d run out of the reclaimed bricks so we couldn’t complete the outer layer fully but Linda has promised to send photos of the finished kiln – I’m looking forward to see the results! More information about kiln building can be found in Joe’s book ‘Kiln Construction: A Brick by Brick Approach’.

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Field: Development into 3D

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.

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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.

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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.

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Slips brushed on White St.T

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.

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Sieving the slaked down porcelain before adding paper pulp
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Glaze mixer

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.

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Inking up the plate

Enamelling

In a similar way to how glaze powder is fused into glass on ceramic, enamel powders are fused onto copper. The temperature however is a lot lower, any higher than 800C and the enamel starts to discolour, as I soon found out.
Before and after shaping the copper needs annealing and then plunging in cold water to cool. Gum arabic is painted onto the back of the shape after cleaning, then backing enamel is dusted on top and the copper placed in a small kiln. When opened the kiln temperature plunges and you have to keep an eye on it as it gradually climbs back up to 799C. On the opposite surface different coloured enamels are fused on in separate firings, although the process is a bit more difficult than I expected. The colours don’t behave as planned, burning out before the kiln reaches optimum temperature or leaving speckled textures (which can look nice – a bit like a dusting of snow).
I’d like to know if these copper enamels can be used on top of bisqued or glazed clay. Alternatively, perhaps panels of enamelled copper (maybe a maker’s mark) could be inlaid into the clay after firing by being stuck on, although I’d have to contest with shrinkage.

 

Week 2 Field: Colour

This second week field project was an introduction to colour theory and the screen-printing process, and for myself an induction into the printmaking workshop.

We started with a colour mixing task. Each person in our group of six was given one of six primary colours in acrylic paint – phthalo blue or ultramarine, cadmium yellow or lemon yellow, cadmium red or magenta then we mixed the exact complimentary of this colour. So for lemon yellow which is towards the bluer end of the spectrum we would make a purple that was more red/pink. Next we mixed the complimentary colours together to get a third shade, and to get a black mixed all three primary colours into one.

SCREEN-PRINTING
Before beginning the screens needed to be cleaned with a water jet set on high and the aid of a cleaning agent. These were then left to dry by the radiator in the darkroom. Once dry a thin layer of emulsion was scraped up to form a rectangle in the centre of the screen using a trough and was left to dry for 45 minutes.

During this waiting time we cut shapes and patterns from black sheets of paper ready to expose the emulsion in the vacuum screen printing press. The cut out shapes were arranged on top of the glass box and the emulsion covered screen was put face-down on top, with a small tube placed inside to aid the vacuum. The screen is exposed to light for 2 minutes during which time the UV light burns away any unwanted emulsion to leave the stencilled shapes. Afterwards we used masking tape to tape around the edges of the screens, leaving a rectangle the size of the paper we were to print on in the middle.

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Our acrylic colours were mixed with the same volume of printing medium and the screens attached to frames over vacuum printing beds. A taped down piece of acetate helped to gauge where to place the paper and then paint was pulled firmly through the screen using rubber squeegees held at an angle. Once we’d ran out of a colour the tape was removed and screen was washed again with the water jet (on a low setting to preserve the emulsion). We layered patterns from the two screens we’d exposed to create prints like the ones below on coloured paper…

The next step was to transform these 2D prints into 3D sculpture. We were shown a Powerpoint about how artists in the past have used colour theory and were particularly drawn to Victor Vasarely’s geometric op art forms. Our final piece is made of 8 separate components which can be seen below, together forming a space-ship shaped mobile. The placing of squares of colour on top of one another was inspired by German artist Josef Albers’s ‘Homage to the Square’ series.

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The process of screen-printing feels quite laborious but once the emulsion has been exposed the screen can be re-used thousands of times. It’s also quite a fast printing process once you get going. I struggled with the technique of pulling down the paint and my first results were very uneven but I found moving to a lower table helped. There’s scope for me to experiment with screen printing slips or glazes onto acetate which can then be transferred onto rounded forms and clay vessels. Slabs could be printed onto in the same way we printed onto paper, then cut up and re-assembled. We used coloured paper and I could even add pigment to the clay itself in the same way to see if this changes the printed surface colours.

Hot melt rubber molds

I took part in my first ‘open house’ workshop today where I learnt how to use the hot melt vinyl compound Vinamold/Gelflex to make flexible moulds. Much cheaper than silicone, it can be used to cast all sorts, from plaster to wax, resins and ceramic material.However it does have some drawbacks, namely that it shrinks over time and when used with plaster or wood they have to be soaked first in water.

The Vinamold is first cut into sugar-cube sized chunks which is a bit of a challenge but is easiest done with a stanley knife and scissors. The texture is similar to that of tough meat. Next it’s heated in the microwave to around 150C which took around 6 minutes for  a full Pyrex measuring jug, a little longer for larger quantities. It’s best to check the consistency every 3 minutes or so in case it begins to burn. The objects we wanted to make moulds of were placed onto sheets of clay with a cottle to give a gap of about two fingers width in between. When the compound was of a runny, soupy consistency it was poured into the moulds and left to set for about an hour. It was easy to release the objects from inside and every tiny detail is captured. The process is so much quicker than making a plaster mould.

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