Wednesday, August 23, 2006

Review of the Tandoor firing.

Phew. The Tandoor was still warm the next morning. And still standing in one piece!

The clay definitely seems solid enough to cook in. You can see that the base is cracked. I'm pretty sure this is because the hot charcoal was sitting directly on the wet clay. It would have been better to use fire bricks for the base as they are already "cooked" and can take the direct heat from the charcoal at the start of the firing. It will still be fine for cooking and the ashes help fill the gaps.

There are some vertical hairline fractures in the pot. I should have massaged the pieces into place more diligently. I think the wet clay I used to pad out the gaps didn't dry properly and this caused the cracking. It should still be fine for cooking though.

The two large cracks on the outside of the pot in yesterday's photo seem to have stabilised. They are probably less than a quarter of the pot thickness. The large cracks look like a problem to do with the clay taking on the shape I wanted. I think maybe either there were air bubbles in the clay, it didn't dry enough or I should have made sure the clay was fully bashed into the curved shape. I think I might fill them with fire cement to ensure there is plenty of strength.

It's worth noting that the pot has shrunk quite a bit during firing. It maybe sits half an inch below the level of the oil drum now. Not a problem, but I'm glad I made it a bit too big in the wet clay.

I think a lot of these problems could have been avoided if I had used fire bricks in the base, worked the clay in the vertical joints more and dried the pot for a week or two before firing.

The final learning is that its not worth doing the coating with jaggery to go up to these very high temperatures. It produced a lot of acrid smoke, carbonised and quite a bit of it started burning. I think it would be better to fire the pot and then do a second cooler firing with the jaggery. At about 200°C the jaggery dries quickly and peels off the clay, leaving a thin sugary layer on the clay - this has to be the right process for lining the pot.

All that said, the pot is definitely good for cooking, and I'm confident its structure will now be stable up to the highest cooking temperatures. I need to work out how to cover the insulation in the top of the pot - fire cement is likely to be the right answer here too.

And of course, I now need to get cooking and for that I need some drier weather again!


Blogger Amanda said...

That is a great post. Well done!
What kind of insulation did you use?

2:47 am  
Blogger bigbrowncow said...

The insulation is designed for building home kilns - it can withstand a much higher temperature than fibreglass.

10:24 am  

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