[silves89]

The raw clay wouldn't be vitrified, so it would be porous and would seep or leak. A glaze is a glass, more or less, and to get the silica to melt you need a flux. There are different fluxes for different temperature firings, but suddenly things are getting a little more precise. Without substantially levelling up the kiln tech and design you'll be at best low-fired and probably using lead as a flux. E.g. terracotta and earthernware.

Early peoples would have used wax or fats to seal pots like these, to make them functional. People do that with modern pit-fired pots too, or use other sealants.

I designed and built my own high-fire kiln, but it uses industrially made light-weight insulating and refractory brick, and gas burners, and I use Orton cones to know when I've hit the right amount of heat-work, and a pyrometer to take temperature readings. But some brave souls make their own bricks, and look at the colour inside the kiln to know when they're at temperature.

[Neil44]

I used to use an electric kiln to do firings for my partner. It was fun working on the process. Our house had a lowish supply voltage so I ran 10mm2 cable back to the consumer unit, and experimented with the impedance of the elements, as we did a lot of quite high firings. I used an electronic kiln controller mostly but occasionally verified it against an Orton cone. Gas would have been more economical but a bit more scary, for me anyway.

[silves89]

It's scary for me too! And way less economical in the UK than electric. My small electric kiln costs £5 to fire. My big (perhaps 4 times the size) gas kiln costs £70-£80.

I'd much prefer firing with wood. But I'm too suburban and firing with wood takes much more effort in prep and during firing, but it's a pleasant and exciting experience! Which gas firing is not.