Slocum stone (sometimes sold as "Slocum opal") is an early opal simulant which was briefly popular prior to the introduction of synthetics and less expensive simulants.Mindat.org entry retrieved 11 November 2009. It was named after its inventor, John L. Slocum (1920–1998)Michigan Obituary and Death Notice Archive retrieved 07 May 2019 of Rochester, Michigan.O'Donoghue, Michael (1997). Synthetic, Imitation, and Treated Gemstones. Oxford, United Kingdom: Butterworth-Heinemann. pp. 133–134.
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"Eckert, Allan W. (1997). The World of Opals. New York, New York: John Wiley and Sons. pp. 107–108. By 1976, this product was being manufactured by MDI Corporation.Kaldis, Emanuel. (1982). Current Topics in Materials Science, volume 10. Michigan: North Holland Publishing Co. p. 483.
Slocum Stone is a silicate glass which shows traces of sodium, magnesium, aluminum and titanium.Dedeyne, Roger. (2007). Tables of Gemstone Identification. Ghent, Belgium: Glirico. p. 281. It was manufactured in several base colors, and the opalescence is produced by very thin layers of metallic film (estimated at 30 nanometres in thicknessO'Donoghue, Michael (2006). Gems: their sources, descriptions and identification (sixth edition). Oxford, United Kingdom: Butterworth-Heinemann. p. 548. ), in the form of translucent flakes, which produce a thin-film interference 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.Read, Peter G. (2005). Gemmology (third edition). Oxford, United Kingdom: Elsevier Butterworth-Heinemann. p. 221. In later examples, built-up laminationsMuseum of Fine Arts, Boston retrieved 12 November 2009. are visible when viewed from the side."Gem Gallery: Opal, Slocum Stone photographs," theimage.com. Archived from the original on 12 November 2009. Retrieved 12 November 2009.
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