Dear Lori,
The subject of vented vs. unvented mold frames has some similarities
to passionate discussions about religion: each side is immovably
convinced of the correctness of its position and unwilling or unable
to listen to the opposite point of view.
Molding technology throughout the rubber industry (non-jewelry, that
is) holds that molds should be closed, without vents, in order to
build up internal pressure in the mold cavity in order to force the
rubber into all the nooks and crannies of the design.
Believers in vented jewelry mold frames seem comforted by the sight
of rubber flowing out of the vent holes: to them this means that all
is well inside the dark and unseen cavity of the frame.
Thousands upon thousands of molds have been made with vented mold
frames and even more without them. Both styles seem to work.
There is a belief in some quarters that rubber shrinkage is reduced
by the use of vented mold frames, but there is no empirical proof of
this. I remember attending an early Santa Fe conference in the 1980’s
at which Louis Sanchez, then at Rio Grande, presented research on
this subject. He compared shrinkage rates for molds made from
unvented mold frames with those made and mold frames with various
size holes in various positions.
I remember well his conclusion: “In conclusion, I have no
conclusion”.
So – whatever mold vent hole religion you belong to, you might as
well continue as you are.
Michael Knight
CASTALDO
www.castaldo.com