Smooth-On urethane casting resin Ultra-Black Pint — fast-curing, 80D hard durable finish

Smooth-Cast Onyx Fast is a high-performance, fast-curing urethane resin in a convenient pint unit formulated for deep black castings. It blends 1A:1B by volume, pours easily thanks to low viscosity, and delivers a dense, opaque finish useful for prototypes, props, small parts, and decorative objects where a consistent, solid black appearance is desired. Designed for makers and professionals who need speed and convenience, Onyx Fast balances short working time with a robust final hardness.

How quickly will Smooth-Cast Onyx Fast cure and how much working time do I have?

Onyx Fast is engineered for rapid turnaround jobs: it has a very short pot life and reaches demold strength in minutes. Expect only a couple minutes of workable time and demolding within roughly 10–15 minutes, depending on part thickness and ambient conditions.

• Pot life (working time): approximately 2.5 minutes
• Demold/cure time: about 10–15 minutes at room temperature
• Room-temperature cure—no oven required for standard cure
• Fast processing suits small runs and quick prototypes

What mixing and pouring steps ensure consistent, bubble-free results?

Mixing is straightforward because the system uses a 1:1 by-volume ratio, reducing measurement errors. Its low viscosity helps the resin flow into fine details, but because the pot life is short, mix and pour promptly and work with small batches for best results.

• Mix ratio: 1A:1B by volume for simple measuring
• Low viscosity for good mould release and detail reproduction
• Stir thoroughly and pour immediately to avoid premature gel
• Consider vacuum or pressure casting for near-perfect surfaces

What are the finished material properties and typical uses?

The cured material is a hard, opaque black plastic with a Shore hardness around 80D, offering improved physical strength and heat resistance compared with many softer casting urethanes. It’s suited to functional prototypes, theatrical props, small tooling, and parts where an intense black aesthetic or light-blocking body is required.

• Shore hardness: approximately 80D for rigid parts
• Ultra-black, opaque finish ideal for non-reflective elements
• Higher heat and mechanical resistance than softer urethanes
• Applications: props, prototypes, housings, jewellery, art pieces

The product is mercury-free and formulated for ease-of-use in studio or shop environments, but always follow safety guidance for urethane resins including gloves, eye protection, and adequate ventilation.

Who is this for? Smooth-Cast Onyx Fast is best suited for model makers, prop fabricators, product developers, and hobbyists who need quick cure times, a rich black finish, and a rigid final part. It’s particularly useful when fast iteration is required or when parts must be produced quickly in small batches. Avoid large-volume pours unless you have experience managing short pot-life resins; for longer working time, consider a slower Onyx variant.