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Silicone molds vs. vulcanized

I couldn’t agree with Les more. I still get free samples of Silicone
to test and compare. I also started using Silastic E RTV in 1977. I
still have many of these mold and they still work to my satisfaction.
I have stated this several times before but the best Silicone to use
is a little hard to find even though it is in the Silastic group. L
RTV is the best of all I’ve ever used. Here is a list of the Silastic
mold material and their properties. All have virtually no shrinkage
and are contaminated by sulfur and gum rubber contact. Shelf life of
about two to three years. I’ve used some real old stuff and still got
good results. I have also put my vulcavizer in storage.

E RTV - White silicone. Easy to cut but will tear at some fine
detail. Fairly fluid. I don’t recommend it’s use anymore. It was the
first Silicone I ever tried.

L RTV - Light green silicone. The best jewelry mold making silicone
available. Pours, cuts and injects great. My silicone standard to
compare all other silicones to. I guarantee if anyone tries this
silicone they won’t go back to anything else.

J RTV - Light green silicone. Looks just like L RTV. This stuff is
good, but MAAAAAN are these mold hard to cut. Very little flex. Good
for real flat objects.

M RTV - Very similar to J RTV. Blue in color. I like this hard
silicone for metal mold making. It delivers great detail in the class
rings I tool. I just make one seam cut and the mold peels away from
the master.

If any of you CAD users want to see this mold process with my class
ring process, I will have a CD Rom Flash presentation done within a
week or two and could send one out. I need postage paid but the CD
will be free. Let me know off line at @T_R_Hawkinson_Ltd1.

Best Regards,
Todd Hawkinson,
T.R. the Teacher
part of the site is now up

As a hobbyist, when I was casting a variety of objects in RTV molds,
I used Legos to make my frames. They allowed plenty of variation in
the size of the mold.

Fernando Vigil

Hi Les, I have a little trick for you to have a RTV mold even faster
then a vulcanisation mold. For the frame use metal and glass parts,
pour and vacuum the mold then put it in the oven at about 100F-120F (
stay under the melting point of your wax!!) You will be able to cut
your mold within the hour! You’ll have to experiment a little
depending on your RTV. If you heat to much and to long the mold gets
hard, but if you time it just right there is no difference, and I do
beat my vulcanizer. Cheers, Klaus

For those of you looking for cheap mold frames for RTV molds. Go to
the local hardware store and purchase some aluminum strips. They
usually come in 6 to 8 foot lengths and widths from 1/2 inch to 2
inches. All you have to do is bend a piece of the appropriate length
into a u shape. Sand down the crimp that is created at the bend
corners so you have a nice flat edge. Cut a couple of pieces of plexi
glas (I use 1/8 inch) to fit each side and clamp in place with a
rubber band or c clamp. I then glue a sprue form button in place at
the bottom center of the frame using 5 min. epoxy. You can make
frames the width, height, and thickness you need with very low cost.
If you use a c clamp instead of the rubber bands you can heat the
molds as long as you don’t heat it hot enough to damage the plexi. Or
you can use glass in place of plexi. I prefer the plexi as the glass
has been know to break when trying to seperate the mold frames.
Frank Goss

Dear Frank, I also make all my own mold frames, but I use precut
brass strips from Micromark. They go on sale once a year and I stock
up. I prefer to cast my own spru buttons and soft solder them to the
bases. If you cut your own frames (unless you have a real accurate
shear) your mold frame will be crooked and leak. The Micromark brass
comes in all widths so the size is uniform. The brass strips are
pretty cheap also, about .85 cents apiece. Quarter inch Plexiglas and
C clamps for me too.

Best Regards,
Todd Hawkinson
T.R. the Teacher

Todd: the aluminum I am talking about also comes in strips so you
don’t have to worry about cutting it except for the length you need
for each frame. Thanks for the tip about the micrmark brass. Frank