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Smooth-Cast ONYX Black Polyurethane Plastic

Regular price $34.99 incl. GST
Regular price $59.99 Sale price $34.99
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  • Trial Size Unit — (1.0 kg.)
  • 1 Gallon Unit — (7.48 kg.)

Smooth-Cast ONYX® is a mercury-free urethane resin that cures at room temperature to a Deep Black, solid plastic. ONYX® resins offer the convenience of a 1A:1B by volume mix ratio and have very low viscosities, so they are easy to mix and pour. ONYX® resins have an ultimate Shore hardness of 80D and offer higher physical properties and higher heat resistance vs. other general purpose resins. ONYX® resins are available in 2 speeds.

Advantages that ONYX® resins offer over other resins:

  1. if you desire a black casting, adding color pigment is not necessary
  2. cured plastic is ultra-black and darker than competitive black resins
  3. cured ONYX® plastic can be polished and buffed to a high gloss shine
  4. ONYX® offers higher heat resistance vs. competitive black resins
  5. unlike other black resins, ONYX® does not contain mercury
  6. ONYX® is less expensive vs. other black resins.

Applications include reproducing sculpture, making prototypes and potting / encapsulation. Due to it's quick cure time and hardness, ONYX® is a good choice for creating fast cold cast bronze, brass, copper, nickel or silver effects.

Customer Reviews

Based on 3 reviews
anthony lindsay
Liquid Plastic


Mike Sinclair
Fast Onyx Black

Have been using Smooth Cast 300 (white) which is borderline too fast to use and this is even faster. Even at 1:1 by weight. So if you need any time to mix etc, use the Onyx Black Slow.

Ian Shand
Easy to use but some stickyness

Works well, easy to use, measure, mix and pour.

One problem for my application - filling in some worn areas in wood - was that, while it cures as stated in the instructions it developed a sticky tacky surface which I'm not sure Ill be able to sand down given the gooey surface,

Fortunately I tried a test application first. Can you offer some advice as to how to overcome this effect.

May need to work out what’s causing this issue. I would start by mixing up a small amount in a cup outside of your wood working environment to see if it cures properly. If so, then it may be the timber causing issues.

The 3 tips to success with these types of products is as follows:

1. Mix ratio: Be sure to follow the mix ratio prescribed on the pack. This can be different depending on measuring by volume or weight. So double check.
2. Mix properly: Always do an initial mix in one mixing container, then transfer this mix into a 2nd mixing container. This will ensure you don’t have any unmixed product in the sides/bottom of the container.
3. Temperature is really important. Make sure both the resin is around 23 degrees before using it, and your working environment. If resin is too cold it cures slowly and the resin will be too thick to release gasses. If it’s too hot the resin will cook off too quick and you will form extra bubbles that will not be able to escape.

Sticky finishes can be a result of all 3 points above if not observed correctly.