Slocum stone (sometimes sold as "Slocum opal") is an early

opal Opal is a hydrated amorphous form of silica (SiO2·''n''H2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Due to its amorphous property, it is classified as a mineraloid, unlike crystalline form ...

simulant which was briefly popular prior to the introduction of synthetics and less expensive simulants. It was named after its inventor, John L. Slocum (1920–1998) of

Rochester, Michigan Rochester is a city in Oakland County in the U.S. state of Michigan. The population was 12,711 at the 2010 census. It is a northern suburb in Metro Detroit located 20 miles north of the city of Detroit. Rochester was the first European settlem ...

. John Slocum experimented during the 1960s with various methods. In 1971, he began marketing his first commercial simulant under the "Opal Essence" trade name. Not satisfied, he continued experimenting and in 1974 brought out the more realistic "Slocum Stone" type. However, Gilson synthetic opals and other imitation opals such as " Opalite" came onto the market soon thereafter and greatly diluted the market for "Slocum Stone" By 1976, this product was being manufactured by MDI Corporation. Slocum Stone is a

silicate glass Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of ...

which shows traces of

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...

and

titanium Titanium is a chemical element with the Symbol (chemistry), symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resista ...

. It was manufactured in several base colors, and the opalescence is produced by very thin layers of metallic film (estimated at 30 nanometres in thickness), in the form of translucent flakes, which produce a

thin-film interference Thin-film interference is a natural phenomenon in which light waves reflected by the upper and lower boundaries of a thin film interfere with one another, either enhancing or reducing the reflected light. When the thickness of the film is an ...

effect. These flakes themselves lend color, along with colorant within the glass base. Bubbles and swirls typical of glass are other typical inclusions which may be noticed under magnification. In later examples, built-up laminations are visible when viewed from the side.Gem Gallery: Opal, Slocum Stone photographs
" theimage.com

from the original on 12 November 2009. Retrieved 12 November 2009.

References

{{Reflist Products introduced in 1974 Opals Nanomaterials Thin-film optics