Kathy, we could go on and on about this one…casting is not an
But, for the basics always add a sprue to the object you are casting
at least as big around as the thickess part of the object and place
it at the heaviest part of the object as well if you can. Obviously
the blended wax should be smooth and depending on the size, shape,
and position on the tree you could get different results on each.
The general rule is the lighter weight objects at the top, medium in
the middle and heavier at the bottom.
To avoid this, cast all the same object. Usually you will have a few
bad ones at the top and the bottom. The sprue on the tree should
have 5 to 10% extra metal for the button. There are other things that
come into play, kind of machine you are casting with, heat of the
flask at casting time, heat of the metal going into the flask, how
long you let it cool before quench, etc. If you want to really learn
it you can go to any school for a casting class. I used to teach this
at GIA in Carlsbad, CA. You also have to make sure of the investment
mix ration of water to investment, the proper mixing time and setup
before popping the flask in the oven.
My inclination at this point to get back to your crevice situation is
that your metal is solidifying too fast which means the metal is not
hot enough or your flask is too cold. This area should be smooth
without porosity or cracks.