Archive for the ‘firing’ Tag

This week I have been mostly making…Glazes   Leave a comment

At last the pottery is fully functioning. It seems to have taken forever to get to this point but I have now done my first successful glaze firing. The sources of delay have been many and varied. There have been the usual decorating and DIY jobs needed when you move to a new home. The very large garden was a wilderness and is now reasonably tamed and producing bumper harvests. We’ve had a continuous stream of visitors all keen to see what we have let ourselves in for. Several of them stayed for long weekends and some friends from New Zealand stayed for a fortnight. Various major remedial works have been completed such as re-roofing the summer house and moving the gas tank (and as a result also the garden tool shed). Major building work has also commenced and is still ongoing. Getting this started has involved much deliberation on how we wanted the internal layout of one end of the house to be changed followed by the process of getting planning permission, choosing a builder, specifying internal fittings, sanitary ware, kitchen units, floorings, wall decoration etc. etc. All in all it has been difficult to spend any consistent amount of time in the pottery.

pottery waterworks

Outside the clay room. The water comes from the roof and is stored in the green water butt. To the right are shelves for drying pots prior to bisque firing and a table on which glazes are made. In the far left foreground is the kiln lid. Behind this are shelves for kiln props and above these the energy regulator which caused the first glaze firing to go wrong. This is attached to the firing controller (the box with its red instruction manual tucked behind it).

Nevertheless, although intermittent, progress has been made on the potting front. After finishing off the clay room I started to throw pots. It was a bit of a shock to find that although some aspects of throwing, such as centring, hadn’t faded away with lack of practice, other skills such as ‘just knowing’ how close to the wheel head  I had pushed my thumbs down when opening out a ball of clay had deserted me. The other vital skill of ‘just knowing’ how thick the wall of a pot is when you are pulling it up had also faded. The first few throwing sessions produced pots with excessively thick or thin bases and with similarly unsatisfactory wall thicknesses. Initially the walls were too thin and the pots would collapse half an hour after they were removed from the wheel. I then had a phase of leaving the walls too thick. I resolved to make sure that every session in the pottery would begin with an hour of throwing practice. Fortunately, after just a few weeks, these skills returned but all the practice did leave me with many tubs of clay for recycling and very few pots which would be consigned to the kiln. Just as well really because the drying/glazing/kiln room was still under construction.

When in the pottery and  not practicing throwing I lined the remainder of the garage walls with battens and insulated plasterboard, shelves and tables. On the outside wall of the clay room I installed a worktop and second hand sink and on the worktop, against the outside wall I built a stand for a water butt. The water butt  is filled by run-off from the roof and with a capacity of 160 litres provides all the cold water the pottery needs. A hosepipe attached to the water butt tap allows me to direct the flow into the sink or to a glaze bucket sitting on the floor.  If I want hot water I just boil a kettle. Underneath the sink is a big water tank where clay and glaze ingredients can settle out before the water  goes down the drain. Finally I wired up the kiln, put it in its final position and put packing under some of the legs to make it level and stable. I then packed it rather loosely with the unfired pots I hadn’t felt needed throwing in the recycling bin, and did a biscuit (bisque) firing to 1000C. All went well. I had the essentials for pot making.

Before I left Cambridge I allowed all my glazes to dry out completely – for ease of transport – so the next job was to reconstitute these with water, which also includes the time consuming job of sieving them. Many an hour was spent stirring the glaze slop to push it through the sieve a pastime which still continues.

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The glazing and decorating area. An old kickwheel I use as a banding wheel, a low table to support the buckets of glaze at a convenient height and shelves holding bisque fired pots awaiting decoration.

As the stream of visitors slowed down and my throwing skills returned I got more time for making and had another kiln-full ready to bisque, However there was one last hiccough to delay full scale production. When I did my last glaze firing in Cambridge it was clear that the kiln elements were worn out. The temperature struggled up to 1240C and took 15 minutes longer than it should have done. One or two of the pots looked a bit  ‘overcooked’. Time for a new set of elements. Replacing the elements themselves is not too bad a job but the kiln’s instruction book said that after changing the elements the kiln should be fired once to 750C while empty and twice to 1000C with pots in before a glaze firing is attempted. Over a period of 3 weeks and with a lot of frantic throwing activity I duly did as instructed and finally was ready to produce a finished, glazed pot.

I glazed enough pots to fill the kiln, carefully selecting those pots which I hadn’t put too much effort into or which, after the biscuit firing were clearly destined to be seconds – bits of lime popping in the clay, warped, non-circular things etc. A first firing with new elements is prone to mishaps!  Caution, pessimism, realism, experience, I don’t know but BINGO! the mishap occurred. The kiln has a single cooker style energy regulator which limits the amount of power going to the kiln. It is also fitted with a programmable firing controller which switches power on and off to achieve the desired firing rate. This makes the energy regulator redundant – it is always left set to full power and consequently I have never needed to consider it since the first day I got the kiln. Unfortunately, at some point in the months since I left Cambridge the setting of the energy regulator got changed and I didn’t notice. Even when the firing controller was trying to give continuous full power the kiln was only getting about 80% power. This didn’t matter below 1000C as the kiln achieves this quite easily, which is why I didn’t notice the problem sooner. However as the temperature got above 1100C the rate of temperature increase fell below what the firing controller was trying to achieve. It was as if I hadn’t changed the elements and despite  frantic efforts to diagnose the problem I didn’t spot the incorrectly set regulator. Eventually the kiln reached the desired temperature but 50% of the pots went straight to the bin and the rest are substandard.

I eventually spotted the regulator problem a couple of days later while cleaning plaster dust off it and was actually relieved to know that the cause of the problem was nothing more serious. The next glaze firing was fine.

I now need to find outlets for my pottery and make a start with preparations for housing, building and fuelling the wood kiln.

Posted October 27, 2013 by damiankeefe in Uncategorized

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