The BVDA America Silmark is a gray-colored silicone rubber casting material. With the high concentration of pigments in the material, even the strong lighting under a microscope cannot penetrate and reflect from particles beneath the surface of the cast and optimum sharpness of the microscopic image is thus guaranteed. The gray color has the advantage of providing an excellent contrast when photographing and digitally storing the casted toolmarks.
The low viscosity variant is for making test impressions in the lab (usually on an horizontal surface), where it will flow easily into the smallest details. For the curing of the silicon rubber a paste hardener is used. The paste hardener is conveniently measured and mixed.