Setting Freeforms

Dear All, A while ago I found a litle article on the net
( by Derek Levin about setting freeform gemstones.
In order to make the bezel, he proposes to use substances which are
normally used by dentists to make mouth impressions for crowns. Two
products are necessary: Alginate, which a sort of rubberized
impression material, and Van-Rock, which is a hard plaster. The idea
is to push the stone in the Alginate, to fill up the impression with
Van-Rock and to go on working with the plaster replica of the stone.
I have been looking at a couple of dental catalogs (von Schein,
Zahn). While Alginate is quite cheap, Van-Rock is not so cheap and
can only be ordered in a large quantity (11 lbs.). Of course, I do
not need 11 lbs. One or two lbs would be sufficient. Does any of you
uses this technique to set freeforms? If not, which technique do you
prefer? I know that it is possible to make the bezel in wax, but I
find this complex. If anyone would use Van-Rock (or something
similar), would it perhaps be possible to buy a little quantity?
Thank you for reading, and with best regards, Will

Doing this would be so very easy at your Dentist’s office. Befriend
the lab tech or dental assistant and ask if they would be willing to
help you do a trial with one stone before you order the items
yourself. If it works well for you, ask if you can buy a few pounds
of stone from them. Ask them for the hardest one they use since it
comes in different hardness’s for different purposes. At most it
would take 15 minutes of their time and very little in materials so
maybe offer to bring in a sandwich and do it on their lunch hour.
They can also show you the correct and easiest way to use the
products. I spent 15 years working in a dental office so this comes
from much experience. I still design earrings on a stone replica of
my own ear made using alginate and stone before I left my job 16
years ago.

    about setting freeform In order to make the bezel,
he proposes to use substances which are 

Alginate is the least accurate material used by dentists for crown
construction and is not used for that purpose by most dentists.
However having said that, it can work in the procedure you describe,
if handled properly. There are many other materials available for
taking the impression of your freeform stones which would work far
better without the dimensions being affected by time and humidity. As
to the high cost of the stone (Van Rock) which was suggested, there
are many manufacturers of dental stones (which is refined plaster of
Paris) which are equally hard. Since the volume available to purchase
is far more than you need, I am sure a visit to your dentist with an
explanation of your problem will result in him giving you on e or two
cupfuls of dental stone. They all have it for making models.

     Does any of you uses this technique to set freeforms? If not,
which technique do you prefer? 

I have made a complicated setting for a laser cut stone by
duplicating the stone using a polysiloxane impression material
(frequently used by dentists for accurate mouth impressions) and
pouring into the impression a plastic material instead of “stone”.
This model was then mounted on the platform of a vacuum forming
machine (another dental tool) and a shell of acrylic is formed which
is the female counterpart of the stones pavilion. This is then
trimmed as desired and is subsequently cast in the desired metal by
investing it as you would a wax pattern and burning out. (good
ventalation required).

I realize this is a rather sketchy desciption, and if further
is needed, please feel free to call upon me.