CS 19 Flashcards
Who created the first marketable synthetic opal?
Pierre Gilson
Play-of-color that’s seen only when light travels through an opal to the eye is called
Contra-luz opals show play-of-color when light is transmitted through them
Plastic imitation opal was first marketed in the late 1980s in
Japan
Opal types are often based on
background color
Most opal formed
7,000 to 110 million years ago. Scientists believe that opal origin dates back between about 7,000 and 110 million years
What is semi-black opal’s background color?
Semi-black opal has a grayish background color
What is the transparency range of white opal’s background?
Translucent to opaque
What is the first step in evaluating an opal?
Determine the type, there are 8
Experts think fire opal’s background color is caused by
Iron impurities
The world’s main source of fine-quality black opal is
New South Wales, AU
Opal is composed primarily of
hydrous silica
Which treatment involves immersing opal in concentrated sulfuric acid?
sugar
What is the transparency of gray-base black opal?
Opaque
In opal, a pattern of large, distinct, usually rectangular patches of play-of-color with edges that touch each other is called
Harlequin
Boulder opal consists of thin layers of precious opal cut to include a matrix of sandstone or
ironstone
