I have a good selection of base colors that Slocum Stone was available in years ago. These stones are very hard to find these days. The colors in these stones are MUCH more impressive than my photos show.
In the early 70's a man named John Slocum was looking to make synthetic opal. What he came up with is an extremely realistic imitation also known as “Slocum Stone” Also referred to as "Slocum opal" and "Opal-Essence"
These stones are an excellent opal imitation with a wide range of body colors including white, black, golden yellow, brown and green. Slocum stone is also much more durable than natural opal.
Slocum stone is a piece of history to the gem world, collectible and pricey if you can find any for sale. The formula was closely guarded and lost with Mr. Slocum's passing.