Post 48 New toy

What do all good marketers say - "buy on emotion and defend on logic". You see I've bought a small kiln. Now I'm a two kiln potter!!!

So my defence of this latest purchase is the intrinsic value I will get out of being able to do small scale firings for glaze, firing schedule and clay body testing. Fire a small number of samples, evaluate and test again without having to wait for the bigger kiln to have a nearly load ready or otherwise fire underloaded. This little one is certainly too small to fire all but the smallest bonsai pots. And how did I get it past the Senate Estimates Committee - well what all good long serving workers would do - make a claim on prior unrealised accrued benefits. It worked for me.

It's a Woodrow Minifire kiln with a firebox that is only 300 x 300 x 150. It comes with its own controller and runs on 240v so just plugs straight into a regular wall socket. At 1800 watts it's like running a big room heater for the duration of the firing, except the 'room' is just that little firebox. No wonder it can get up to 1280C in there.

In the picture you can see I've mounted it on a small trolley so it can be wheeled away and stored, works well. It only weighs 25 kilos but there's just no way to pick it up. That little white plug on the top is the vent.

It's had it's first test firing - I took those clay body additive test samples of Post 47 through the glaze firing schedule. The little programmable controller works a treat.

Post 47 Slumping test

Some time ago I posted about Pyroplastic Deformation with a picture showing how the bisqued clay could deform under the glaze firing conditions. That test sparked a little research and an idea to test a number of ceramic materials as additives to the clay body to assess any impact on the slumping character.

I started with 8 materials, then realised I needed a control sample, then read about grog and silica sand. That resulted in 10 samples, listed in the table below.

Thes pictures show the sample bars arranged in 'bend order', best at the front to worst to the back, in the above picture and clearly left to right below.

It is interesting to observe a change in colouration too. The bars which have deformed the most have darkened in colour. The additives in these bars have obviously 'fluxed' the clay; in effect enabling the clay to mature at a lower tempreature than without the additive. The one doubt about this conclusion is that the worst two have relatively high water absorption or porosity (for stoneware).

At the other end of the scale, the two sand additive bars, have shown the lowest deformation and the highest absorption, which will eliminate these as prospects. The control absorpton result was 0.8% which is very good.

For the best 8 samples the deformation difference between them isn't really signifiacant. So if that's the case then the next level of selection is water absorption. On that basis Kaolin is the one that stands out. Perhaps this should be no surprise as Kaolin is basically quite refractory and is a key ingredient in high firing ceramics.You might expect that it would elevate the maturity temperature, but the absorption is unchanged for the control sample.

Further reading suggests that you may need to get to 10% additive before really seeing the impact of many materials. I can feel another test series coming up - next time to evaluate a number of different levels of Kaolin addition and bringing in another test - shrinkage as an additional indicator of maturity.

Post 46 Four more new pots

I'm catching up on my backlog of bisqued pots. Only 2 more on the shelf now so will need to get on and make more.

The extensive glaze development and trial work has paid off. I have a couple of formulations now that will produce good stable outdoor glazes, with subtle tones and a surface with just a hint of satin. With the investment in time and resources to get these larger pots to bisque, it is a leap of faith to take a glaze that looks ok on a 35 x 50 test tile and put it on a pot. The dynamics in the kiln can produce a contradictory result. But fortunately with these 4 the result has been very close to the test result and just what I've been aiming for.

Pot 26 First of this new design and a little shape challenged without the external rim. I'm going to have to put one on the inside in future. The glaze is great and one I will certainly use again. The pot is 335 x  235 x 77, a little smaller than the others that follow.

 

 Pot 22 Came through really well and a good glaze. This more traditional pot shape seems to call for a darker colour and the brown works well. Final size at 377 x 274 x 91.

 

Oval Pot 24 with a nice differentiated cream/beige glaze breaking to sienna has the appearance of patination. I have profiled the pot wall with a lapstrake pattern to get that break and it has worked out well. Final size is 410 x 299 x 84.

Pot 18 has been hanging around for a while waiting for its turn in the kiln again. The wait was all about getting the right darker toned glaze which took some trial work. Same shape as no 22 finished up at 380 x 278 x 91. The picture doesn't do the glaze justice; a very attractive finish with evocative colours that shift with the lighting.

I made 2 new pots last week, currently drying, which takes the number to 30. 30 pots over 18 months has been a good apprenticeship and while the learning goes on I have reached a point where I think I can with some confidence in the result, turn out saleable quality pots.