Crystal Clear® 221

Crystal Clear® 221

Crystal Clear® 221 is a water white clear resins made specifically for applications that require absolute clarity. These are “heat cure” systems and are harder versions of our popular Crystal Clear® Series resins (Shore 85D).

CAUTION: NOT FOR HOME USE. THIS PRODUCT IS FOR INDUSTRIAL USE ONLY. Proper ventilation, A NIOSH Approved Respirator and Protective Clothing (gloves and long sleeves) are required to minimize the risk of inhalation and dermal sensitization. If breathing is affected or a dermal rash develops, immediately cease using this product and seek medical attention. Read SDS before using.


Cured castings are:

Vibrant colors and color effects are achieved by adding pigment dispersions. Applications include encapsulation, making prototype models, lenses, sculpture reproductions, decorative cast pieces, jewelry, special effects and props.


Safety - Store and use at room temperature (73°F/23°C). These products have a limited shelf life and should be used as soon as possible. Environmental humidity should be as low as possible. Good room size ventilation is essential. Wear safety glasses, long sleeves and rubber gloves to minimize contamination risk. Wearing a NIOSH approved respirator will minimize inhalation of residual fumes.

Selecting A Mold Rubber - Pour into a urethane rubber mold (Vytaflex urethane – release agent required), tin cured silicone mold (Mold Max® silicone) or Mold Star® 15, 16 or 30 (not Mold Star® 20T) platinum cured silicone. Do not use other rubber mold products. If you are unsure about surface compatibility, a trial casting should be made. To prevent cure inhibition, post-cure newly made Mold Max® silicones for 8 hours at 150°F / 60°C and let cool prior to casting resin.

For Best Results: Pre-heat the rubber mold at 212°F / 100°C for 4 hours before mixing & pouring Crystal Clear®. This will minimize the chances that cured castings will exhibit casting phenomenon such as fish-eyeing, suck back, corner rounding, large bubbles, etc.

Liquid urethanes are moisture sensitive and will absorb atmospheric moisture. Mixing tools and containers should be clean and made of metal or plastic. Materials should be stored and used in a warm environment (73°F / 23°C).

Measuring - Materials should be stored and used at room temperature (73°F / 23°C). The proper mixing ratio is 100A:75B by weight. You must use an accurate scale (gram scale or triple beam balance scale) to weigh these components properly Dispense the required amount of Part A into a mixing container. Weigh out the appropriate amount of Part B and combine with Part A.

Mixing - Mix SLOWLY, but thoroughly, for at least 90 seconds making sure that you scrape the sides and bottom of your container several times. If coloring or filling Crystal Clear® product, add filler or pigment dispersion to Part B and mix thoroughly before adding Part A.

Bubbles in the finished casting will be greatly reduced by vacuum degassing prior to pouring. Subject mixture to 29 h.i.g. mercury in a suitable vacuum chamber for until mixture rises, breaks and falls. Allow for 3 to 4 times volume expansion in mixing container.

IMPORTANT: Shelf life of product is reduced after opening. Remaining product should be used as soon as possible. Immediately replacing the lids on both containers after dispensing product will help prolong the shelf life of the unused product. XTEND-IT® Dry Gas Blanket (available from Smooth-On) will significantly prolong the shelf life of unused liquid urethane products.

Pouring - If casting Crystal Clear® into a rubber mold, pour mixture in a single spot at the lowest point of the mold. If encapsulating an object, do not pour the mixture directly over the object. Let the mixture seek its level. A uniform flow will help minimize entrapped air.

For Best Results: Bubble elimination is best achieved by pressure casting. After pouring the mixed compound, the entire casting assembly (mold, dam structure, etc.) is placed in a pressure chamber and subjected to 60 PSI (4.2 kg/cm2) air pressure for at two hours prior to heat curing.

Room Temperature Cure - Followed By Post Cure - Allow material to cure overnight at room temperature (73°F / 23° C). Place entire mold structure in an oven and cure at 150°F / 60°C for 4 hours, followed by 4 hours at 212°F / 100°C. Allow casting or part to cool to room temperature before demolding.

Heat Curing - After pouring material into pre-heated mold, heat cure for four hours at 212°F / 100°C. Allow casting or part to cool to room temperature before demolding.

Because no two applications are quite the same, a small test application to determine suitability for your project is recommended if performance of this material is in question.

Related Categories: Urethane Resins and Coatings

Related Series: Crystal Clear™ Series – Water Clear and UV Resistant