Vintage 21x16mm Czech lampwork millefiori black glass over metal cabochon mosaic tile jewelry making

One 21 x 16mm vintage Czech lampwork millefiori black glass over metal rectangle cabochon mosaic tile. These are highly elaborate, starting with a metal base onto which is set cane and colored sections of overlay glass and then heated to fuse all the components together.
The making of these cabochons was very labor intensive, so these stones were used in either precious metal or in very fashionable costume jewelry settings in the vintage jewelry era. 
These can be bezel or prong set and as the base is metal, they can be soldered to connector loops or shanks to make necklaces, earrings and bracelets.
Important to note- these are handmade and each will be slightly different. You will receive one from the lot in the images which are representative only. 

Size: 21 x 16mm. 13/16" x 10/16". 3mm thick
Material: Glass
Condition: Vintage condition. 
Quantity: 1