Specifications include, but are not limited to: Glass spheres shall be transparent spheres meeting the following requirements. Refractive Index The spheres shall have an average index of refraction not less than 1.50 when tested by the liquid immersion method at 25 degrees centigrade. ; Imperfect Glass Spheres The glass spheres shall not contain more than twenty (20) percent irregular particles when tested by ASTM D-1155. Imperfect glass spheres are defined as spheres which are ovate or otherwise nonspherical in shape, two or more beads fused together, opaque spheres or pitted spheres. Moisture Resistance Spheres shall pass the “Free Flow Test”. ; 1. Standard one-pint screw cap mason jars with two piece covers consisting of a flat cover plate with sealing gasket attached and a crew ring to hold the cover plate on the jar.