This is information about homemade crucibles based on my own experience
First of all let's decide why one may want to make a crucible for the wootz or steelmaking.
The SiC brand made crucibles are available and they work very well. They
can be even reused if handled carefully.
The only problem is the price. If you are fortunate it may serve you for
many (up to a dozen) melts. But if it
cracked after you removed first ingot - it will be VERY
When I started to make wootz I've read a lot of articles. All of them described the
disposable crucibles that were broken after the melt and dumped. So for me it was no question if the crucible has to
be used only once.
My first crucibles were made of Mullite and EPK Kaolin. At first I used about 7-8 parts of Mullite
and 2-3 parts of Kaolin. The mixture was very sandy, the green (unfired) strength was bad but the crucibles stood well in fire.
Later I started to add graphite and changed the ratios to 5 parts of Mullite, 4 parts of Kaolin and 1 part of graphite powder.
Mullite is a Alumina Oxide and Silica Oxide composition. It has about 60% of Alumina and 40% of Silica Oxides and very few other impurities.
That makes it very good base and filler for the clay. Kaolin is cone 12 and higher refractory clay with very good plastic
Graphite needed mostly to neutralize free oxygen inside the crucible during the melt and add some "flexibility" to the crucible walls.
It is the only element that shrinks with temperature and prevents cracks.
I use very simple mold made of 4" PVC pipe and wooden insert. The wooden
dowel helps to
ram the mixture in the mold. It is more important to pack the clay mixture evenly than
tightly. Uneven density cause cracks. I used hydraulic
bottle jack to press the clay but found it less
efficient than just few blows of 1lb hammer. Hammer works even better and way faster.
The ready crucibles must dry in cold place for at least a week. I dry them in my garage. After a week the crucible can be heated in
the kitchen oven for a few hours at 350F. It is not unreasonable to heat it already charged and covered with the lid so you put
it in the furnace for the melt completely dry.
At some point I decide to look for cheaper substitution for the Mullite
quite expensive. Potters use "grog" as a filler for their pottery. Is is fired to high cone
fireclay or crushed firebrick.
It comes in different mesh numbers and is really cheap. I tried to use the same
recipe replacing Mullite with grog.
The crucibles were standing in fire and everything looked good
until I started to forge the ingots. They all failed sooner or later. In
most cases the steel billet split before was forged into the blade. Some billets cracked after the heat treatment. Some had very bad
intergranular cracks throughout the blade. I did not get single blade forged from the ingots made in those crucibles.
After some research I concluded that grog may be too porous and gases (oxygen in particular) can get in the crucible and make some damage
to the steel. I also think that brick grog that I used can have unknown and harmful contaminants.
Recently I returned to my old recipe and everything is back to normal.
Sometime I would like to try to make pure Alumina Oxide crucible with Phosphate binder.
Do not have recipe yet. If it will work and have some benefits over Mullite-Kaolin crucibles I will post a note.