Saturday, February 27, 2016

Resin casting 101: pouring the resin

There's more than one way to make a resin. Some people use a roto-caster, which results in a  lightweight, hollow cast model. Jennifer Scott prefers to use an air compressor and pressure tank (also called a pressure pot or casting pot). The filled mold is placed inside the pot, and the pot is closed. The air compressor forces air into the pot, which shrinks the air bubbles in the liquid resin to microscopic proportions. This creates a solid cast, but extremely clean model with no pin holes.
Jenn's resin of choice is Smooth-Cast 305. She likes it for its whiteness, strength, sandability and seven minute pot life. She used to use Smooth-Cast 300, which has a two min pot life, but she prefers having more time to mix, pour, fasten and fill the tank. Trying to do all that in just two minutes was crazy and stressful!
Different resins have different mix ratios, but Smooth-Cast 305 is 1:1 of Part A and B. Jenn likes to "cross the streams" as she pours for added mixing. As soon as the two parts combine, the clock starts ticking!
 Mix very thoroughly...
and then it's time to pour. Because she's pressure casting, she doesn't have to worry about degassing the resin or pouring in a slow, thin stream.
This particular mold uses a hind leg for a pour hole.You can see the other hind leg's air vent at the bottom of the photo.
When the mold is filled with resin, it's pushed back into the pot and the lid is fastened via the wing nuts. Everything must be good and tight before you start letting air into the tank.
Pressure casting requires at least thirty psi of pressure to work, but sixty psi is ideal. Jenn's tank tank is rated for up to eighty psi, but since there's no quality difference between sixty and eighty, she uses the lower setting.
It's better to mix too much resin than too little. However, resin is expensive, so Jenn pours the excess in a small medallion mold.
These will be wonderful live show prizes!
The mold will stay inside the pressurized tank for approximately forty minutes, so there's lots of time to cuddle Jenn's studio helper while waiting for the new arrival.
The third and final part of this series will cover removing the new resin from the mold and basic clean-up. Thanks again to Jennifer Scott for making these posts possible!


  1. Thank you for sharing the process! It's really interesting :)

  2. one of my favorite parts of the artistic process is seeing the dichotomy between how detailed and precise the mold is, with everything done so very very carefully... while the resin is mixed and poured with solo cups and an old popcorn container. i love it haha

    1. To be technical, it's a *new* popcorn container. Jenn bought a large lot of them for a ridiculously good price, so now every Aspen Leaf horse starts life that way!

    2. Ahh... it's wonderful knowing that your ponies started life in a *new* popcorn container :)

      An amazing article!

  3. The dixie cups get expensive and they're not big enough to hold enough resin for one solid traditional horse so I looked for an alternative to at least a mixing cup. A case of 500 of the solo popcorn cups were found! :) And I can reuse them. <3

    1. ha that's awesome - and is exactly my favorite kind of creative practicality ;)

  4. Every studio needs a helper and companion (usually of the adorable canine persuasion :))

  5. LOL I have those exact same popcorn cups and I use them for vacuuming my sillicones!