I took in a job the other day that required me to duplicate a ring
in platinum. It had some tricky freeform curves that wax carving
wasn’t getting for me, especially du to the fact it’s not easy for
me to “over polish” them metal to achieve the rounded flowing look.
Anyway, I decided to try the no shrink pink rubber to get the 0%
shrinkage. I don’t use a vulcanizer but an oven and I use C clamps
to hold the plates together. It’s worked fine for me for years. I
calibrated my oven with my digital pyrometer from my casting oven
and set the temp at 315 according to customer service at Castaldo.
The oven was cycling between 306 - 325. I baked it for 45 minutes
(5 sheets 1/8 thick) and it came out with tiny bubbles everywhere
and REAL soft. Tried again at 310 (cycling between 298 - 317) and
no bubbles. The only problem was when I started to cut it, it was
like chewing gum. REAL soft and pliable. I got pissed off and
ripped it apart with my hands to get the model out and went back to
my silicone. It had a little shrinkage, but my friendly wax pen
helped build up the thin spots. Anybody have an idea what went wrong
with my pink mold? Do I have a bad batch? Is this normal? I did
notice that after the mold (or what is now a lump of pink rubber) is
harder than what it was when it was warm. Not sure if it has to
cure a bit longer to gain it’s composure. Please let me know your
thoughts before I return this stuff back to RIO.

Travis Duggan
Placitas, NM

The Castaldo No-Shrink Pink mold rubber will produce very precise 0%
shrinkage molds if processes are followed exactly. The product
specifically states that precise temperature control is required for
this product. You also need to accurately calibrate your vulcanizer
to exactly 310F.

I calibrated my oven with my digital pyrometer from my casting oven
and set the temp at 315 according to customer service at Castaldo.
The oven was cycling between 306 - 325. Tried again at 310 (cycling
between 298 - 317)

Cooking molds in your oven can work if the temperature is exact.
The problem with the oven you cook a cake in is that it has hot
spots. As you get closer to the heating elements the hotter it is.
The side facing the elements can be hotter than the side away from
the elements. There can be as much as a 50 degree variance within
the oven depending on the type, age, and placement in the oven.
Opening the door also can affect the heat within the oven. This
method will work for rubbers that do not require such precise
temperature control but the no-shrink pink states that it requires
very precise/exact temperatures. You can always call Rio Grande for
technical support or since you live here stop by if your on this
side of town. I hope this helps.

Phillip Scott
Technical Support & Sales
Rio Grande

Hey Travis, What was the phase of the moon the night you made your
mold? :slight_smile:

With that aside, try your oven at 320 F, and leave it in for twice
as long (1.5 hours). The reason for this is that you’re relying upon
air to heat up your mold plates/frame, as opposed to the direct hot
metal platens of a vulcanizer. Essentially, air, being at the same
temperature as metal, has much less energy than the metal, which is
why you’re getting incomplete vulcanizations.

NSP is not nearly as forgiving as many mold-making materials. I
would attempt it one more time (or two) using these guidelines - or
something similar.

I’ve never tried this in an oven before, so you’ll have to take it
at face value.

If I were you, I’d make an RTV (cold mold) mold, and not expect NSP
to produce 0% shrinkage.

Matt Feliksa President Golden Sun MFG., Inc. “Specializing in platinum
casting to the trade.”