All seasons of the history of art were characterized by the use of hard stones that, alongside the main disciplines of art, were often used by their availability and technical knowledge acquired at the time.
During the Middle Ages, began to spread in paintings the use of the hard stones in order to embellish the ornaments and the meticulous finishes of the golden leaflets.
More than a simple precious decoration, precious stones gained a higher value by affirming themselves as symbols of a humanity who felt the urge to be purified and found in the purity and perfection of these stones the sign of virtue, as in the case of crystals, especially of the Rocca Crystal, sought after in the Middle Ages and throughout the sixteenth century, a representation of perfect virtue.
It was therefore not a case that in the Christian iconography, the precious stone was assumed as a symbol of Mary, being able to shine only when struck by the ray of divine light.
The precious stones world was invested with a strong symbolism that Christian authors sought to "clean up" from the superstition patrol inherited from earlier times to accentuate the symbolic value.
An ever deeper bond, destined to grow in virtue of the particular properties of precious stones, characterized by transparency, color, hardness and ability to be imperceptible, unlike all other creatures of the earth.
Of all the stones, the most appreciated in the Middle Ages and in the Renaissance was certainly quartz, in particular hyalenic quartz or rock crystal, with opal, aquamarine, jasper, amethyst, agate and corniola.
Not less appreciated were coral and pearls, also featured with a strong symbolic meaning.
Coral was, in fact, the symbol of Christ's blood and its function was of protection, while the pearls, which were considered gems of the sea, were regarded as the emblem of virginity and purity and for this reason associated with the Virgin, brides but also to kings and princes.
A world loaded with symbologies of precious stones that, in the various fields in which they were engaged, from ornamentation to painting had the task of meeting a decorative and ornamental demand and assuming a symbolic value, able to unite the sense of magic with religious meanings.
An example of the strong link between precious stone and symbolism is found in the Apocalypse of John, where the Holy City, New Jerusalem, is described with a splendor "similar to precious stone, as shining stone as a crystal."
" The walls are built with jasper and the city is pure gold, similar to crystal clear.  The foundations of the city walls are adorned with all kinds of precious stones. The first foundation is of jasper, the second of sapphire, the third of the calceon, the emerald quarter, the fifth of sardonice, the sixth of sardine, the seventh of the chrysolite, the eighth of beryl, the ninth of topaz , the tenth of chrysoprase, the eleventh of hyacinth, the twelfth of amethyst.  And the twelve gates are twelve pearls; Each door is made of one pearl. And the city square is of pure gold, as a transparent crystal, "