Synthetics and Imitations
When is a gem not a gem? When it's a synthetic or an imitation. Are those the same? Nope. Synthetic gemstones are man-made, but have the same chemical composition and structure as the natural gem. Imitations are just that...some other substance that looks like (to some extent at least!) and pretends to be the nature-created gemstone.
Historically, gemstones have been an easily portable form of wealth. We've all heard stories about refugees fleeing with diamonds sewn into hems. Since gems are easily portable and of high value, it inevitably follows that some people will try to pass of imitations or synthetics as the real thing.
But, this is a big but, synthetics and imitations are not intrinsically bad. It's only when they're made/sold with intent to deceive that the whole business of right and wrong comes into the equation. Sometimes a substitute 'gem' is the result of ignorance and sometimes it's a good idea. Way back when, all green gems were known as emeralds, even though there are many other green gems. And one of the rubies in the British Crown jewel collection, the Black Prince's Ruby, has long been known to be a spinel. And think of the many elegant ladies who have had their jewelry copied with not-real stones to deter thievery!
One of the very popular imitations, rampant in Victorian times, was the garnet-glass doublet. Some families spent their evenings working together to pour glass into gemstone-shaped molds that had a very thin slice of garnet in the bottom. When cooled and taken from the mold, voila, a gemstone! The bulk was inexpensive glass, and the flat top, known as the table, hard, scratch-resistant garnet. The garnet slice in these doublets is so thin that the color of the gem depends on the color of the glass. Amethyst and peridot were the most popular and many lovely pieces of jewelry held these doublets rather than the real thing.
And sometimes just plain glass was used as an imitation, as is the case in this pretty Art Nouveau lavalier!