I do make projects with precious stones sometimes.
Here is one of the latest ones: a silver, gold gilded ring with a deep violet coloured amethyst.
This high setting of the stone allows the light to make all those beautiful reflexes with in the stone - giving more "life" in it.
For comparison - the ring from the Erfurt Treasure I try to reproduce. Only the gold setting with the stone survived the band probably was cut away and re-melted or re-used for other piece of jewellery.
I am often asked about which gems where used in Middle Ages. That a good moment to put here a little more information about it.
Most of the precious stones used in medieval jewellery was imported from the Far East. From the region of India, Afghanistan, Burma, Sri Lanka. Some where also mined in Europe, like garnets. They came from region of Bohemia (Czech Republik) which made them much available and affordable, that is why they are among the most popular of stones used in jewellery.
The shaping of the stones was still a new and a costly craft in 14th and 15th century, so most of the stones are being left in their natural shape just polished to give them more shine. This type of stone shape is called cabochon.
Here is a few more examples of similar rings with different types of stones.
Another gold ring from the same Erfurt Treasure with almandine ( a type of garnet).
The knowlege of different types of stones and how to check their quality was a important knowlege for many merchants. I one of the letters from 1440 a Florentine merchant Giovanni da Uzzano, shares his opinion about the most desirable precious stones in all colours and how to judge their quality.
"Fine rubies should be like goodly pomegranate seeds,
good balas-rubies should be like a pomegranate that is not well ripened,
a good emerald will show greener than any other green it is laid beside,
a good topaz is like shining gold, and most of them look as if they are split.
A good sapphire resembles good azure pigment, and is on the white side,
a good aquamarine is like sapphire, but more whitish,
a good citrine looks like wax, with something of red in it,
a good garnet looks like a peach flower.
A good diamond looks like steel and is tranlslucent like glass, and has sharp points,
but another sort tends towards yellow, and third sort looks like crystal, though in shape all three are alike.
A good jasper is green, with shining spots, and seems oiled-most of this sort, comes with figures; another kind is brownish green, with red spots.
A good chalcedony is either white with a shade of blue, or white with a shade of yellow.
A good cornelian looks like cherries that are really red.
A good amethysts are violet colour.
A good turquoise looks dove-white in colour and is not transparent."
Lightbown, R. W.: Mediaeval European Jewelry . London 1992
Mecking, Oliver (el al.): Der Schatzfund - Analysen - Herstellungstechniken - Rekonstruktionen. Die Mittelalterliche Judische Kultur in Erfurt, Bd. 2.Weimar 2010.