Mold making & RTV

Jewelry Discussion
1

John and others who might know:

I thought that the vulcanized compounds were used because in a
production situation they keep the costs down — aren’t the RTV
compounds consdierably more expensive??

I don’t cut molds yet, but those who do tell me that they change
blades after every mold or two. A box of blades isn’t that
expensive.

I couldn’t believe it when someone wrote they didn’t cut molds
because they might cut their finger — first, you’re a craftsman
(or craftsmann) you should be able to manage and ashamed to admit
it if you can’t. Second, when you learned to peal potatoes, didn’t
your mother tell you to cut AWAY from your hand??

Just my $.02
Roy (Jess)

2 
John and others who might know:

I thought that the vulcanized compounds were used because in a
production situation they keep the costs down --- aren't the RTV
compounds consdierably more expensive??

G’day; I have to pass on this one - I haven’t done any casting.
Cheers

   /\
 / /

/ /
/ /| \ @John_Burgess2
(___ )
At sunny Nelson NZ (only we’re getting much needed rain right now)

3

vulcanized rubber is used in production work because it has a
greater shear strength than liquid rubbers. Tom

4

I use the RTV instead of vulcanizing because its easier to use,
needs no cutting (unless you like to subject yourself to
bloodletting), needs no special equipment and if purchased from a
manufacturer, is easily comparable to the “old” rubber method or
perhaps cheaper. What more can I say? If you want the name of a
manufacturer, let me know. No heat, no electricity, no special
mold frames.

5

Roy (Jess),

Vulcanized materials are not that much cheaper than the RTV’s
especially if you are compairing prices to some of the new
vulcanized silicons. There is no additional equipment needed (the
vulcanizer) either. I just like the RTV’s as they , at least for
me, are so much easier and seemilgly, for me again, foolproof.

John and others who might know:
I thought that the vulcanized compounds were used because in a
production situation they keep the costs down — aren’t the RTV
compounds consdierably more expensive??

I find that the RTV materials cut easier than the vulcanized
molds. There are numerous hardnesses available in the RTV’s, more
than in the vulcanized.

I don’t cut molds yet, but those who do tell me that they change
blades after every mold or two. A box of blades isn’t that
expensive.

Yep, blades are 10 15 cents each and at that price well worth
saving one’s finger. Don’t forget to lubricate the blades, huge
difference (be careful if you are not used to lubricated blades,
you might cut yourself.)

I couldn’t believe it when someone wrote they didn’t cut molds
because they might cut their finger — first, you’re a craftsman
(or craftsmann) you should be able to manage and ashamed to admit
it if you can’t. Second, when you learned to peal potatoes, didn’t
your mother tell you to cut AWAY from your hand??

Sometimes you can’t always cut away from yourself when cutting
molds but just being very careful and very aware of where the blade
is going to go if it slips or cuts through will eliminate most
problems. I will say a potatoe peeler is nothing like a sergical
knife when it comes to cutting oneself.

John

John and Cynthia/MidLife Crisis Enterprises
Maiden Metals/C. T. Designs/ Bloomin’ Wax Works. etc.

PO Bx 44, Philo
CA 95466
Ph 707-895-2635 FAX 707-895-9332

The playfulness of the Universe
is reflected in the dance of the stars!

6

Vulcanized materials are not that much cheaper than the RTV’s
especially if you are compairing prices to some of the new
vulcanized silicons.

So why do casters charge more for the RTV molds (the 2 casters I
use here in NY charge $15 for a vulcanized and $20 for “silicon”)?
Especially if the RTV is so much easier to use and requires no
special treatment. Is it just because it is a new-fangled
convenience that they could charge more for it?

Jill
@jandr
http://members.tripod.com/~jilk

7

Hi Folks, I have to jump in here…Rubber is still the choice of
the professionals. They are quicker, have less mold shift (parting
lines) and last much longer (if kept out of the sun). RTV molds
are the best alternative and good for beginners because the start
up costs are much less (if you don’t use a vac) I use RTVs for
large objects and also for “organic” things that won’t take heat
and pressure. An experienced mold maker has a battery of mold
making equipment, skills, and materials. Pros and beginners alike
can have big fun with RTV, Mozeltov. J.A.

8

Jill,

See the other posts on this. As to the higher charges, I wouldn’t
know why they do it except for the reason you suggest. The most
expensive part of making a mold if for sure the labor, not the
materials.

John

John and Cynthia/MidLife Crisis Enterprises
Maiden Metals/C. T. Designs/ Bloomin’ Wax Works. etc.

PO Bx 44, Philo
CA 95466
Ph 707-895-2635 FAX 707-895-9332

The playfulness of the Universe
is reflected in the dance of the stars!

9

Hi Jill, I’m going to jump in here. A large percentage of the
molds sold as “Silicon” (especially in NY) are actually a poly
based RTV. Silicon is more expensive. The poly based RTVs Work
just as well and usually bypass shrinkage concerns as do the true
silicon variety and tear less. In my experience, rubber molds hold
up better to production use. I have several RTV molds in my
cabinet made by various moldmakers that are begining to
deteriorate. When a poly based RTV mold goes bad it is usually
because it wasn’t measured and or mixed properly. A mold like this
can work fine for a while and then start to go gooey. There are a
couple of “Not Silicon” RTVs. I have loosely called them “Poly
Based”. I am not a chemist. To learn more about the composition of
these products you can get their MSDS forms and find out what’s in
them. Some of them contain Isocyanates as curing agents and others
are true Polyurethane products. I find “True Silcon” tears much
easier than natural rubber or other RTVs… I can make a rubber
mold for long term production use in a fraction of the time it
take to make an RTV mold. However if you do not have a vulcanizer
and you only need a mold occationally for limited production RTV
is the way to go. As an asside, I use a vulcanizeable silicon
rubber often for flat pieces and powder separation molds. J.A.

10

Hi All- P&G Industries makes a groovy little bench pin with a small
cresent wrench attached to hold corner of a mold when cutting. Its
cheap and really helps hold it all to avoid slicing your fingers.
I bought in 90’ so I am not sure they are still around… P&G
Industries, Inc. po box65099 San Antonio, TX 78265

tlee