Using plaster-based molds for glass casting is an art. A variety of processes can be used to accomplish this feat, however, two are fairly common. The first process involves creating an open-faced mold using a pattern that can be physically removed. The second common practice is creation of an intricate mold that requires the removal of the pattern by heat or steam (lost wax casting).

The plaster-based mold material is mixed with the appropriate percentage of water. This slurry is then poured around the pattern and allowed to set or harden. After proper curing, the pattern is removed by pulling it from the mold, by steam removal, or by heat removal. After the pattern is removed, the glass can be placed in the mold. Again, the method of glass placement varies from artist to artist based on preference and experience.

Ransom & Randolph mold materials stand apart from other materials available due to their superior strength and detail reproduction, allowing for molds that resist cracking and minimize entrapped air. No matter which method of pattern removal is used, R&R’s products work exceptionally.

Below is an overview of the R&R GLASS-CAST mold material product line. At R&R, we have been serving glass casters worldwide for over 10 years and pride ourselves on providing casters with consistent, quality products and excellent customer service.

Zhermack Jewelry Molds 005

R&R GLASS-CAST 910 is R&R’s benchmark mold material. Developed over 20 years ago for casting difficult aluminum aerospace parts, the product became a staple in the glass casting community. Now, R&R produces millions of pounds of R&R GLASS-CAST 910 a year - strictly for casting glass!

R&R GLASS-CAST 910 is widely recognized as the strongest mold material available for glass casting on the market today. This is the glass caster’s best choice for large pieces or configurations that will place significant stress on the mold material.

R&R GLASS-CAST 965 was developed over 25 years ago for industrial casting. The product quickly became a staple for glass casters as well. 

R&R GLASS-CAST 965 is not as strong as 910 investment and is more permeable. Casters have noted that this makes it easier to remove from their finished pieces. This investment is ideal for medium to large size molds.

R&R GLASS-CAST 400 is a stronger, economical mold material. This product has been used successfully in Europe for over 5 years. R&R GLASS-CAST 400 provides added strength for the glass artist that struggles with mold integrity due to mold size or process intensity.

R&R GLASS-CAST 101 is an economical, all-purpose mold material for kiln casting/slumping of glass. It has very fine particles, providing the smoothest of surfaces. R&R GLASS-CAST 101 has sufficient strength for most glass castings of small and medium size. It is the investment of choice for open-face molds and small molds made using the lost wax process.

R&R RTV HT33 silicone rubber is an excellent option for creating a reusable rubber mold of original artwork. R&R RTV silicone rubber is easily mixed together and poured around artwork. After four hours, it is set and ready to be cut away from the original, leaving a hollow cavity for wax reproduction of the original. R&R RTV silicone molds are highly resistant to storage conditions and can be stored and reused up to 20 years.

R&R AquaSphere wax is very fluid once melted, reducing air bubbles at the pattern surface and allowing for easy flow into tight areas. R&R AquaSphere wax characteristics allow for excellent detail and dimensional reproduction from the original silicone mold.  

R&R Mold-Mix 50/50
mold material.

The basic blend glass casters typically start with -
fresh from our manufacturing facility. 

R&R Mold-Mix 50/50 comes
pre-mixed, and
with pre-identified working and setting times.

If you’re not ready to
step up to an R&R Glass-Cast mold material,
this product is a basic
formula to get started in
glass casting.

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