How can I make my casting look like marble?

Article courtesy of Smooth-On, Inc.

Creating a realistic cast marble effect is possible with Smooth-Cast 325 liquid plastic, Ure-Fil 7 filler, and So-Strong colorant.


Ure-Fil 7 is mixed with Smooth-Cast 325 casting resin until the mixture is thick and creamy. This mixture is then simultaneously cast with black pigmented Smooth-Cast 325 to create the "veining" effect commonly found in marble. Getting the effect you want will take practice and we offer the guidelines below as a step by step outline to get you started.

Materials Needed

  • Smooth-Cast 325 Casting Resin - recommended because it is "color neutral" and readily accepts powders and/or pigments.
  • Ure-Fil 7 - Ure-Fil 7 should be completely free of moisture. Ure-Fil 7 is available from many Smooth-On distributors. Call our technical help line to find your nearest distributor.
  • SO-Strong Color Pigment (black or other dark color)
  • Rubber Mold
  • Mold Release Agent - Use only a release agent specifically made for mold making and casting such as Universal Mold Release or Ease Release 200 (both available from Smooth-On and its distributors).
  • Measuring and Mixing Containers
  • Mixing Sticks

Amount of resin, Ure-Fil 7 and pigment required will vary depending on the desired effect. You will have to experiment by varying the amounts of resin, Ure-Fil 7 and pigment used in combination to attain an effect that suits your application. Measuring can be done by volume.  For this example, we will use the following:

1A:1B:2 Parts Ure-Fil 7
Liquid Pigment: 1 drop per 2 oz. / 56 grams resin

Marble Casting Steps

  1. Apply release agent to rubber mold. If casting into a urethane rubber mold, prevent resin mixture from sticking to rubber mold with application of a spray mold release agent into mold cavity and all surfaces that will contact the resin. Brush lightly and follow with second light mist coating. Let dry for 20 minutes.
  2. Create Ure-Fil 7 and Part B Pre-Mix. Mix Ure-Fil 7 thoroughly with Part B of Smooth-Cast 325 (Blue Label). Dispense 1 part of Part B into clean mixing container. Add 2 parts of Ure-Fil 7 and mix thoroughly. The consistency of the mixture will be very thick.
  3. Combine Part A & Part B (with Ure-Fil 7) and mix thoroughly.
  4. Create a color concentrate for veining.  Dispense a small amount of Smooth-Cast 325/Ure-Fil 7 mixture into a separate mixing container. Add a few drops of So-Strong colorant. Mix thoroughly. This color concentrate will be added to the larger white batch of Smooth-Cast 325/Ure-Fil 7 prior to pouring.  You can use other SO-Strong colors besides black to create the vein; green, blue, red, etc.
  5. Drizzle color concentrate over white Smooth-Cast 325/Ure-Fil 7.  Slowly pour the color concentrate in a thin stream, moving the stream randomly over the surface of the white Smooth-Cast 325/Ure-Fil 7 mixture in the larger mixing container.  DO NOT DISTURB OR MIX AT THIS POINT
  6. Pour the entire mix into mold.  Pour the entire mix into the mold in a random pattern while filling the mold.  This technique will create the swirl or "veining" effect that is commonly found in marble. As we said earlier, achieving an acceptable veining effect may take some practice.
  7. Allow casting to cure before demolding. Remember, the resin/Ure-Fil 7 mixture or filled resin will take longer to harden than unfilled resin. Cure time depends on size of casting, mold configuration, amount of fillers used, etc. Generally 30 to 40 minutes is a sufficient amount of time. Applying mild heat will accelerate cure time. Let cool to room temperature.
  8. Demold the casting from mold.  Lightly polish casting with a wax until the desired luster is attained.

This FAQ article is offered as a guideline and offers possible solutions to problems encountered during mold making and casting. No warranty is implied and it is up to the end user to determine suitability for any specific application. Always refer to the provided Technical Bulletins (TB) & Safety Data Sheets (SDS) before using any material. A small scale test is suggested to determine suitability of any recommendation before trying on a larger scale for any application.