Pros and cons of fuels

Over Easter I fired fibre and brick kilns, with varying degrees of success.

The gas kiln is always easy, being gas, but brick and fuel kilns are a different matter. After about two years of experimenting with different fuels, I have decided to go back to diesel for the following reasons...sure, sump oil from a local garage is a free fuel source, its viscosity is also good, being mixed oils and transmission fluids. All of these burn extremely well and it gives a certain sheen to a glaze like only oil can, but it would have to be one of the most filthiest substances known to man. It's also quite possibly carcinogenic and turns the potter pitch black. After working with how clean gas is, I would prefer it to be like that for the brick kiln.

Which brings me to... vegetable oil mixes; the best one being a 50-50 mix of diesel plus canola oil from the local fish and chip shop. This also burns good and gives nice results,  but it has to be mixed and for best results put through a filter so as not to clog up (even slightly) the taps and burners. This can be time consuming, unless one enjoys this sort of thing.

The final straw for me was when it came to what was taking place in the fuel tank. I thought viscosity was the problem, then I saw the crap that came out of the tank! I had put clean canola oil in and it grew some sort of green algae slimy shite and a lot of it - that would slow down the flow somewhat. The sump oil had also left behind metallic dregs like small flakes and even little twists of metal, that looked like little snails, all packing down into a solid mass at the bottom of the tank. Sometimes being frugal doesn't always pay off,  but you have to try these things to see what does.

Preheating fire box .In this firing, I came in with desiel at about 300 degrees centergrade.

Once the diesel took hold I could control the rate of firing, just like the gas kiln, going from 300 C to 1300 C in around 8 hours.

Lunchtime in the best of company.

Silvery sunset.

Watching cone 8 go over, about to throw the salt in for one hour, just after sunset. As for atmosphere, it was going to be oxidised but with opening and closing the dampner and winding the fuel up till it looked like a dragon breathing through it (reduced),  or knocking the fuel back to slow it down a bit, creating a crystal-clear (oxidised) atmosphere inside, who knows what the outcome will be?

Interesting results and heaps of beautiful glaze tests to analyze.

Some of the better pots from the kiln, alongside cones 8, 9 & 10.

Diesel simplified things so much, no clogging of taps and burners, no oil slick all over my face, arms and legs, and the results were awesome. It's as close to using gas as I can get without using gas. It's worth the extra outlay to be problem-free.

A spot of maintenance

It's easier to repair a pyrometer in the daylight than in the middle of the night in the dark and pouring rain...

bits in pieces.

Hmmmm... blue cheese and chicken, mushroom pizza and ham cranberry [plum,apricot] cream cheese garlic,oregano etc pizza washed down with a good larger or two.

Early morning start up blending with the morning mist, reminiscent of a battle ground scene...

our sleepy hollow looking east, workshop center left.

A large goat lives on the bluff up behind the kilns, he seems to have a lot of leisure time on his hooves, where he sits for hours cross legged. This morning I have caught his attention.

works as good as new

Slow and Steady

It's been a busy year so far. I tried but failed at using canola oil as a fuel for the brick salt-glazing kiln - viscosity issues - so not enough flow, but since it is a medium-sized kiln I had a go anyway.  It basically blew itself out, but no great loss that some work was damaged, as I'm still interested in the test tiles that are still in there. I have already mixed up a test fuel to fire up this weekend if the weather holds out.

I enjoyed firing up some large terracotta pots in the gas kiln. It's so good not having to mix some (sometimes filthy) fuels together, soooo clean...so easy, and also cheap as [efficient]

Spyhole on the gas kiln- 800 deg. celsius and cooling.

Bottom shelf of the 'crypt' (salt glaze kiln) plus test tiles and clay sheath [top left] to protect the probe from salt.

If only it was like this all the time!

Bursting, stony texture from local clay straight out of the ground.

When the sun hits these pots, they heat up like they're just  fresh from the kiln - the burnt caramel look is as pleasant on the eye as any glaze.

Like a painter who does portraits of people, I like to make portraits of great pots in three dimensions.

Rough and ready

A quick post on salt firing...

In this photo I have cut a bottom shelf  and placed it on some props.I have also installed a crude bagwall.This time around I hope to not fire too much over 1300 deg c. because it plays havoc with my  kiln shelves making them hard as. If anyone out there has experienced cutting silicon carbide with a masonry blade you will know what I mean...The heat...the dust and these shelves aren't light either.

Tomorrow I will cut a third shelf and work on the chimney, kiln wash the shelves, etc and on next day - glazing and packing. Hopefully I'll be ready to fire up on the weekend, although I was planning a trip down the harbour to gather some cockle shells (for that nice wadding effect that everyone does) and a trip to a local forest for some pine needles for my raku firings. Good thing I'm not in any kind of a hurry... rough enough.

Merry Xmas, happy pizza oven

Last week I helped my sister build a pizza oven in her back yard. It is quite a complex structure consisting of a dome and two arches covered in refractory concrete. Here are some pictures of the process that I'll try to explain as I go...

The smaller arch is half bricks, the bigger arch is full brick except the two at the top are three quarter to leave a space for the chimney. Using all straight bricks to save cutting or shaping any I also used plenty of a home-made castable in the gaps,the same mix I use for my kilns.

Tina built the stone walls where she wanted the oven situated and had everything measured up and ready to go, arches cut, etc. The design is one from 'The Shed' a NZ handyman magazine. After she'd done the wall, my Dad laid the concrete slab.  All I had to do was come along and place out and lay the bricks.

First layer of bricks placed out to fit the two arches so we could slide them out easily. To the left of the arch you can see the gaps filled by the castable mix.

With the two arches in place, we then started laying the dome. It was quite hard to figure out how to tie it into the arches but again, this is where the refractory stuff comes in handy. My sister Mandy arrived and split some red bricks.

On Christmas morning, we went round to Tina's to remove the templates for the arches. A photo of Mt Cargill we took on the way.

Checking out the castable mix, which consists of local terracotta clay, beach sand, straw and cement.

Me and Tina removing the outer arch template by taking out two screws and dropping the template down. It came out no problems at all.

The inside of the oven. We used fire brick for the first three levels, or basically until we ran out, then we used house bricks for the rest.

A little fire of newspaper just to try things out, and dry everything slowly.  Works sweet, would make a great raku kiln. Can't wait to try out a pizza!

View from the car on the way home down Old Brighton Road.

Rainbow above the kiln on a dark and brooding day.

Recent work awaiting firing.

This oven would be a great design for a raku kiln. It was good to see my pottery and kiln building skills used outside of ceramics.

Happy New Year! All the best for 2012.

Now focus...but, hey, whats that...?

Sometimes I have trouble keeping my eye on the prize. With at least four different clay bodies, all maturing at different temperatures and glazes from 1000c to 1350+,  things soon get a little overwhelming...So today I decided to try and keep it simple with a solo raku firing.

After work in the morning, I stirred up some glazes from earlier in the year and applied them to some raw pots I made over the last couple of weeks and spent a sunny afternoon doing what I enjoy most - glazing, stacking, firing, and unpacking, all in the same day.

But before I start rambling, here are some photos of the day's happenings:

Raku stack ready to go with cone 06 in position.

The all important items and essential firing charts.

The fickle Dunedin weather goes something like this-Monday hot and sunny about 32 deg.C with a coastline like the Mediterranean  (minus the people). Good for surfing. By Friday, snow to sea level - an  unexpected surprise in the late spring, even though they said it was coming.

After a short jog along the beach while the pots were cooling off in the reduction bin, and a quick scrub, I was pretty happy with the outcome.

Man, I could raku all year with these kinda results...But what's that, is that about 150 salt glaze tests ready to fire, oh well here we go again!

Tools of the trade and stuff

Another good day spent pottering about. Some people talk of their approach to potting,whether it be London, Paris, Tokyo or New York, local markets and galleries, or making things for oneself and a few others.  The equipment and tools we use and the wheel spinning around remain constant. For me, I enjoy the lifestyle it brings and as a enthusiastic hobbyist I love all the chemistry of mixing glazes, building and firing kilns, the sometimes dramatic or subtle results. It's great just to have the chance to make something beautiful. I'm glad I don't have to do it for a living, I have a part time job for that, but it's great to have a hobby that could possibly become a means to an end or a supplementary income if I can get it to that level and that comes down to productivity and how much you push yourself, head per capita etc.etc.

So i guess I would consider myself a part time pottery enthusiast but with a passion for clay and fire and fulfillment.Something I'm sure every potter can relate to at one time or another. On to some pics with captions

Down here I work with white clay for now,so I've washed some tools after using buff and red clays and these are some of the tools I make and use often.

Soft and loose bottle forms to be raku fired for eggshell like glaze effects, or salt glazed for a more stony texture.

The weather shot

Since bricks are getting scarce I will be dismantling a kiln once more for other projects. In this frame one can see the arch is of straight brick with castable key wedge in the center .This saves cutting bricks and can be used anywhere. Below that is the flue exit and some chimney bricks sticking out. Under the flu exit is the floor bricks and under that is where the flame enters from the firebox, runs under the floor into the kiln.

Looking in from the front seeing where the flame combusts  under the floor. .In this photo I removed 5 firebricks from the  floor and at the rear is the flue exit.

In this kiln the floor bricks are still in place showing where the flame will enter and exit, and a salt port. Needs a bottom shelf so the heat will need to go under it to escape and a bagwall

I will use the bricks from the other kiln for a chimney along with a length of flue and more bricks for the door (wicket). It has a small fire box to prime the throat for the burner, 0 to 500 or 1000 deg C on wood depending on the size of the firebox, 400 to 1350+ on oil slash diesel.  I have never had the patience to fire on wood alone as after 1000 deg it gets hard work. This kiln is designed for oils and would need a big firebox as close to the kin as possible (or even under it) to run on wood alone for stoneware temperatures.

random size lumps of white clay, by tomorrow they'll be pots.

Supermarket plastic bags and polythene buckets store clay well.

Burner, fuel line,tap,hose,tape, bag of salt...check.

old vacuum blowers, check.

Props, shelves, shelf wash, fire clay, wadding, check

Fuel-tank.

Disused long-drop - self explanatory.

Walkies.

A guy showing his 4 year old daughter to surf. The sea's been pumping lately and she caught a couple of mini tsunamis like a pro. Impressive.

Now glazing, firing charts, throwing... stuff for another time. Getting late, Gotta sleep.