It depends. If you allow for shrinkage, it shouldn't be a problem.
If the original wax is uniform then there will be uniform
shrinkage. If the wax model is irregular there can be some
distortion, but there are tricks around this problem. I can be as
simple as putting other pieces in the same flask to keep the heat
even. Never done this myself, but an old founder told me some
interesting stories.
Shrinkage is not uniform, ever, it is dependent on surface area to
cross section relationships along with mold thickness and model
placement in the mold etc.
A paper presented at the Santa Fe Symposium on Jewelry Manufacturing
and Technology by Tyler Teague of JETT Research showed that using a
silicon rubber mold from original model to finished ring there were
the following changes
Id: Model 19.95 mm, Wax 19.88 mm, Casting 19.63 mm, Finished 19.82mm,
Change.65%
Width: Model 4.05 mm, Wax 4.00 mm, Casting 4.12 mm,Finished 3.82
Change 5.68%
Thickness: Model 1.93 mm, Wax 1.98 mm Casting 1.91 mm, Finished 1.72
Change 10.88%
Weight: Model 5.930 gm, Wax n/a, Casting 5.877 gm, Finished 4.907
Change 17.25%
And you can with careful measurement easily see what the results are
in your studio, they may be similar but not exactly the same and
there are many factors that will affect the results, rubber type, wax
temperature and pressure, flask temperature, metal temperature just
to name a few.
Most jewelers just don’t take the time to do these measurements. In
very high tech models there is a lot of work done to counteract this
but it takes a sophisticated computer modeling and still a little
trial and error to get it right for any given model. For jewelry
most times it is not an issue because we do not work to those kinds
of tolerances. But for aerospace or medical devices or other
demanding products a lot of work goes into trying to deal with this.
Leonid is right about sharp edges they will round off in any casting
and there is not a thing you can do about it. Individual jewelers for
the most part don’t bother with these issues because most are not
demanding enough of their castings. In industrial jewelry though a
lot of time and effort goes into accounting for shrinkage to try to
limit the amount of time needed to finish an item as the margins on
mass produced jewelry don’t allow for the time that a typical studio
goldsmith puts into tweaking and finishing a casting. So while you
may feel that your castings are near perfect reproductions if you do
the work to measure them you will find that there are significant
differences in section from model to finished work.
The assertion that one can mold and cast a copy of Leonid’s ring or
any other object and achieve an exact copy is just BS. Can you come
close, and make an item that the majority of jewelry buyers would
see as being the same? Yes, but if you were to measure and examine it
with magnification it would be obvious even to a casual observer
which was the casting and which was the original. Is one better than
the other? That is a judgement that depends totally on what your
criteria are. For simple shapes where access by tools is possible
then you can finish a raw casting that has enough mass in the right
places to be virtually equivalent to the fabricated piece by lots of
filing, sanding, carving etc. But if it is a highly textured or
finely detailed object there is just no way to achieve a similar
piece because you just can’t get the as cast surface finished to the
same quality as the fabricated item.
There are a myriad of examples of fine work in both cast and
fabricated jewelry as well as a lot of crap. So as others have said
make good work and lets quit beating this dead horse.
James Binnion
James Binnion Metal Arts
