Join Date: Feb 2006
Location: 30 miles north of Bangkok, 20 miles south of Ayuthaya, Thailand
I had tried a couple wootz smelting with no success. And what I can tell you is that button shape crucible 's much more easy to work with.
First of all, oxygen protection is a must for wootz smelting. In wootz furnace, the crucibles are required to be arranged at the combustion zone (highest heat, ~1400 C). Since atmospheric condition 's not totally reduction, molten steel surface need to be protected and minimized.
The second reason is for the crucible 's stability, as Jeff mentioned. Even modern refractory get soften a bit at that temperature. Wootz crucibles are need to be heated at 1200-1300 C for several hours. Good design 's required or crucibles will be fail (very messy, 'liv me).
Third reason 's also ceramic thing. The fact that the higher refractory materials has lower plasticity and green strength 's another major constrain for their shape. You cannot make a very complex shape. And cup-shape crucible 's difficult enough for hand-forming pieces.
The forth reason; dendritic steel 's VERY difficult to forge down, especially when heat 's required to be under 800 C. Even with annealed button, smiths may require 30-40 reds (heat cycles) to forge button flat. That 'coz of dendritic structure 's required to be broken into small. And after the button has been "forge soften", only another 10-20 reds to go to bar or other shape. If the metal was made as bar, 50+ heat cycles still need for shaping.
The metal cannot be cast to shape 'coz the "as cast" material 's too brittle for any application.