Casting porosity in Silver

HELP !!!
I am casting silver using a vacume caster and am getting porosity ( very
small pits ) they seem to pop up during the last part of the finishing.
I am using an electro melt and melting around 300 grams of silver at a time.
I am sure I am spruing the pieces correctly . What am I doing wrong ? ...
Thanks

Dennis Montilepre wrote:
HELP !!!
I am casting silver using a vacume caster and am getting porosity (
very small pits ) they seem to pop up during the last part of the
finishing.
I am using an electro melt and melting around 300 grams of silver at
a time. I am sure I am spruing the pieces correctly . What am I doing
wrong ? ... Thanks

Probably soluted gas in liquid silver will be ejected druring cristalization
process. And get in solution by remeltig again. :-(

There are three possibilites to clean from soluted gas:
1. Overheating for some minutes with several hundred degrees. (works low)
2. Cleaning by cristalization in one direction. Pour it into a iron form and
hold the surface fluid as long as possible. (e.g. gas burner) Three times
is most enough. (works better)
3. Use degassing flux http://www.butschal.de/werkstatt/englisch.html
http://www.butschal.de/werkstatt/pr.html#ac (works best) ;-)

--
Heinrich Butschal
casting technologies
http://butschal.de/werkstatt