---
product_id: 458820556
title: "Smooth-Cast Onyx Fast - Ultra-Black Urethane Resin (Gallon Unit)"
brand: "smooth-on"
price: "S$508"
currency: SGD
in_stock: true
category: "Smooth On"
url: https://www.desertcart.sg/products/458820556-smooth-cast-onyx-fast-ultra-black-urethane-resin-gallon-unit
store_origin: SG
region: Singapore
---

# Deep ultra-black finish 10-15 min fast cure 1:1 easy mix ratio Smooth-Cast Onyx Fast - Ultra-Black Urethane Resin (Gallon Unit)

**Brand:** smooth-on
**Price:** S$508
**Availability:** ✅ In Stock

## Summary

> 🖤 Cast in Black, Cure in a Flash — Own the Night!

## Quick Answers

- **What is this?** Smooth-Cast Onyx Fast - Ultra-Black Urethane Resin (Gallon Unit) by smooth-on
- **How much does it cost?** S$508 with free shipping
- **Is it available?** Yes, in stock and ready to ship
- **Where can I buy it?** [www.desertcart.sg](https://www.desertcart.sg/products/458820556-smooth-cast-onyx-fast-ultra-black-urethane-resin-gallon-unit)

## Best For

- smooth-on enthusiasts

## Why This Product

- Trusted smooth-on brand quality
- Free international shipping included
- Worldwide delivery with tracking
- 15-day hassle-free returns

## Key Features

- • **Effortless Mixing:** Perfect 1A:1B volume ratio with ultra-low viscosity for smooth, bubble-free pours every time.
- • **Mercury-Free & Safe:** Work confidently with a non-toxic, mercury-free formula designed for professional studios and workshops.
- • **Rapid Room-Temp Cure:** Get solid, deep black parts in just 10-15 minutes—no oven needed.
- • **Durable & Heat-Resistant:** Shore Hardness 80D delivers tough, long-lasting parts that withstand higher heat than typical resins.
- • **Versatile Creative Power:** Ideal for sculptors, modelers, and prototypers craving flawless black casts that stand out.

## Overview

Smooth-Cast ONYX Fast is a mercury-free urethane resin that cures rapidly at room temperature to a deep black, solid plastic. Featuring a user-friendly 1:1 mix ratio and low viscosity, it enables quick, easy pours with a pot life of 2.5 minutes and full cure in 10-15 minutes. With a Shore Hardness of 80D, it offers superior durability and heat resistance compared to general-purpose resins, making it a top choice for professional artists and modelers seeking high-performance black casts.

## Description

Smooth-Cast ONYX is a mercury-free urethane resin that cures quickly at room temperature to a deep black, solid plastic. ONYX offers the convenience of a 1A:1B by volume mix ratio and has a very low viscosity, so it is easy to mix and pour. POT LIFE: 2.5 mins; CURE TIME: 10-15 mins. , SHORE HARDNESS: 80D and offers higher physical properties and higher heat resistance vs. other general purpose resins. Consult the Technical Bulletin for more information. Read the MSDS sheet before using. Visit us at: www.smooth-on.com

## Features

- PRODUCT PURPOSE: Smooth-Cast ONYX is a mercury-free urethane resin that cures quickly at room temperature to a deep black, solid plastic
- KEY SPECIFICATIONS: mix ratio and has a very low viscosity, so it is easy t, working time 2, cure or demold 10-15 mins, hardness 80D
- VERSATILE APPLICATIONS: POT LIFE: 2.5 mins
- WORKABLE PROCESS: ONYX offers the convenience of a 1A:1B by volume mix ratio and has a very low viscosity, so it is easy to mix and pour
- FINISHED PERFORMANCE: , SHORE HARDNESS: 80D and offers higher physical properties and higher heat resistance vs

## Technical Specifications

| Specification | Value |
|---------------|-------|
| ASIN | B0B2YMG461 |
| Best Sellers Rank | #62,961 in Arts, Crafts & Sewing ( See Top 100 in Arts, Crafts & Sewing ) #394 in Sculpture Modeling Compounds |
| Customer Reviews | 4.6 4.6 out of 5 stars (327) |
| Date First Available | February 24, 2014 |
| Manufacturer | Smooth-On, Inc. |

## Images

![Smooth-Cast Onyx Fast - Ultra-Black Urethane Resin (Gallon Unit) - Image 1](https://m.media-amazon.com/images/I/41jWWhVGtGL.jpg)

## Available Options

This product comes in different **Size** options.

## Questions & Answers

**Q: Is this product and the 80D hardness suitable for casting automotive / tractor steering suspension bushings?**
A: for suspension bushings, I think you would be looking at something much more like a 60-80 Shore A, instead of 80 Shore D. Here's a chart: https://goo.gl/images/Yo0hnp

**Q: how much is there?**
A: 1 lb each

**Q: Can this be used to make  longboard wheels?**
A: If a proper mold is used, this material will harden into any desired shape. Although the shrinkage is minimal, I would suspect shrinkage should be taken into account when molding something as precise as a wheel. Whether the material holds up to the rigors of longboarding is questionable. The material is quite hard when fully cured. I haven't looked at the spec sheet in quite some time, but the cured product definitely feels harder than skateboarding wheels, and considerably more brittle. I would suspect the finished wheel would slide quite a bit. Hope this helps.

**Q: Is the final mold heavy? (Ex: mold size 11x6x2)**
A: If the final casting is 132 cubic inches - as you indicate - the piece would weigh 4.76 pounds

## Frequently Bought Together

- Smooth-Cast Onyx Fast - Ultra-Black Urethane Resin (Gallon Unit)
- Smooth-Cast 300 - Bright White, Ultra Low Viscosity Liquid Plastic - Gallon Unit
- Rebound 25 - Brushable Platinum Silicone Rubber - Gallon Unit

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*Product available on Desertcart Singapore*
*Store origin: SG*
*Last updated: 2026-11-13*