Castaldo pink rubber

Hi, I would like to know about your experience with pink castaldo
rubber mold. I read Castaldo’s instructions about vulcanization and
it is not clear. Does 7.5 min per layer at 310 degres is correct or
there is a special way to use it to obtain minimum srinkage.

Guy Audette
Quebec city

Dear Guy,

This is Michael Knight at CASTALDO. 

If you look at the instructions again you will notice that the

temperature recommendation of 310 degree F is suggested as a
STARTING POINT for developing your technique.

No Shrink Pink is extremely sensitive to temperature variations and

requires fairly precise temperature control. Most vulcanizers are of
very poor quality in this regard. I’ve seen brand new machines with
differences of 10, 20, 40 and, in one case, 90 degrees between the
top and bottom plates. And forget about the dial setting – it’s a

The above is the reason our instructions cannot say:  do this and

you will get zero shrinkage. It’s impossible for us to write
instructions that take into account the eccentricities of your
particular vulcanizer.

But 1,000's of mold makers have learned to use the product -- it

takes a while but it’s worth it.

The procedures is outlined in the instructions:  calibrate your

vulcanizer as recommended. Then make a mold, measure shrinkage,
increase temperature a few degrees, make another mold and so on until
you get the results you want. Then do that every time.

Please note that wax injections will shrink a a great deal in the

first 5 minutes, more in the next 5 minutes, and so on at a declining
rate for DAYS. So make a strict practice of measuring shrinkage under
the same conditions and at the same post-injection point. That is, if
you measure your wax 10 minutes after injection, do that exactly for
the rest of your experiments. If you measure one after 5 minutes and
the next one, because the telephone rang or something, after an hour,
you have measured nothing useful.

You can all me at 508 520 1666 if you want to discuss this further. 

	Michael Knight
   Hi, I would like to know about your experience with pink
castaldo rubber mold. I read Castaldo's instructions about
vulcanization and it is not clear. Does 7.5 min per layer at 310
degres is correct or there is a special way to use it to obtain
minimum srinkage.

The main thing to know is that you MUST use the temps given for
noshrink pink, if you are to get little or no shrinkage. This
rubber, unlike virtually all other mold rubbers, really does mean
it’s temperature range quite precisely. Normal vulcanized rubbers
have a relatively generous lattitude in temp within which they’'ll
vulcanize reasonably the same as they did with slight other temps in
that range. the no shrink pink will show measureable differences in
shrinkage with as little as a ten degree difference in temp. You
need an accuratly controlled vulcanizer, which is capable of holding
the right temp consistantly, and where both platens are pretty close
to the same temp (A lot of vulcanizers put the control on only one
platen, and the other is slaved to it, but can still vary quite a bit
in temperature.) And use a good thermometer to check the temp.

All in all, it’s a LOT easier to use the silicones, either
vulcanized or not. they can give you no shrinkage too, with a lot
less pickiness.

Peter Rowe

Hello Guy, I have used the No-Shrink-Pink for many years now. I make
a pink mold on the average of one a week. It did take some
experimenting at first to get it right. I have learned a few tricks
that can help. First you need to calibrate your vulcanizer, if you
have not already done so. Here is the procedure for that. (it is a
good idea to do this even for Gold Label and White Label rubber as
well) First you need an accurate thermometer. I use a long stemmed
one from my wax pot. Radio Shack sells a digital one that is quite
good. I have calibrated mine with a digital one so that I know it is
accurate. You’ll need a small block of wood; about 3" x 4" x 3/4" to
insulate the top heat platen from the bottom platen while checking
each in turn. Some vulcanizers have two controls (one for each
platen) others just have one. If yours has just one control, find the
platen that cycles the highest and set the temp on that one. There is
a light that goes out on most models when it reaches the temp set on
the knob. Watch your thermometer closely and you will notice that the
temp will continue to climb for a few seconds even after the light
has gone out. Find the highest part of the cycle and adjust the knob
accordingly. 310 F is a good starting point. I use 308 F. If your
machine has two knobs repeat the process for the other platen. You
can experiment with different temp settings ONLY after you can
confidently calibrate for a precise temp. I find a shorter cooking
time works better. I cook a 3/4" thick mold (7 pieces of rubber) for
45 mins. I also room cool the mold instead of quenching it. I cook
one mold only at a time instead of using a multiple mold frame. I
have better control on the results because of the different heat
zones on the press surfaces (check it out with your thermometer by
using the above technique and moving the probe around the surface)
You will find the edges are cooler than the middle. Another thing
about the pink stuff is that you’ll need to change blades more
frequently when cutting. I have been able to achieve about 1%
shrinkage with the pink. Ring sizes don’t change but keep in mind
that your injection wax can shrink a lot, especially if you pull the
wax pattern while it is warm and let it cool on the bench. Some
injection waxes shrink more than others. I have several pots with
different waxes that have properties that I can exploit to their best
use. Castaldo makes a Gold injection wax with very good dimensional
stability. Let your pattern cool in the mold a while before pulling.
The Gold wax can be too brittle for filigree but every wax has it’s
tradeoffs. I hope some of this helps. John, J.A.Henkel Co., Inc.
Moldmaking Casting Finishing, Producing Solutions for Jewelry Artists