Specialty Glasses

Aventurine Glass is man-made paste with the addition of fine copper spangles. The reddish brown variety is sometimes met with under the name gold stone or gold star stone. Spangled-aventurine-effect is due to triangular or hexagonal scales of copper. The blue variety (lapis imitation) is colored by cobalt and will appear red under the Chelsea Color Filter.

Slocum Stone is a recent (1976) opal imitation named after its Canadian inventor. It is a composite paste, probably consisting of a body of crown glass of low R.I. (about 1.52) and melting point, into which are pressed fragments of thin films of blown glass of differing R.I. Colors are probably due to interference between layers of differing R.I. The diagnostic features are flow lines and bubbles distorted by pressure during manufacture. Slocum stone triplets are now on the market as well. Slocum stone has been marketed under the deceptive name 'Opal Essence'. Slocum stone can be an extraordinarily good opal simulant. It is reported that the results of production can vary from batch to batch. Some stones display pinfire-type play of color; others may show much broader triangular flashes of color. The background may be black, translucent or nearly completely transparent like fine crystal opal. Low power magnification under the gemological microscope will reveal the twisted tinsel-like nature of the color flashes.

Rhinestone refers to transparent paste which, colorless in the main, shows patches of various colors. Most specimens consist of a thin metallic film which has been vacuum-sputtered onto the surface of the glass thereby causing iridescence.

Imori Glass or Meta Jade is a partially devitrified, translucent green glass produced by Imori in Japan. Slow cooling cause partial crystallization, which often appears as a dendritic (fern-like or tree-like) structure under magnification. The stones may show gas bubbles.

In some cases asterism is obtained by engraving fine, intersecting lines, or by impressing three sets of intersecting lines, on the back of a cabochon. The stones then are frequently backed by colored foil to lend color and increase reflectivity. On the other hand, cat's-eye-like effects can be obtained by the incorporation of parallel glass fibers or by the elongation of included bubbles.