weight of clay

[Zebnon]

1 brick (1kg? 2kg?) = 1 clay
1 pipe — 2 clay
1 mug — 2 clay…
1 smelter = 22 mugs? 50 mugs? just imagine ore smelter and mug…
too much for pipe or mug.

The second thing: why i can build oven/smelter only with bricks? how about clay? how about time for drying and hardending?