Hi Bnh, I believe your problem may stem from the bracelet being too
close to the flask (minimum of 3/4")and possibly not enough head room
(from top of wax to top of flask, a bare minimum of one inch, more is
better). Not to worry, I have the solution. Go to the hardware store
and purchase 6" of fiberglass rope, the kind that is used on the door
of a wood stove. Use some stong shears and cut it all up into 1/4"
pieces. Mix all this into your powder before you add it to the water.
You may find you need a bit more water, have some handy to make the
investment pourable. I use this method for casting large things with
deep undercuts. You may want to use a power mixer to mix thoroughly.
This method adds the "rebar" to prevent cracking. You could also try
using a much larger flask and slow down your burnout. 2hrs @ 300F,
2hrs @ 500, 2 hrs @ 700, 2 hrs @ 1000 climb to 1350 hold for 2 hrs,
Don't open the oven but let it cool to casting temp and hold 1hr.
John, J.A.Henkel Co., Moldmaking Casting Finishing