What materials do you think were used to make this?
This lovely piece is from Doodad Mosaics using some sort of resin.
Here is their site, says they are using found items. Very cool!
http://www.doodadmosaics.com/
Here is how to do it yourself!
https://www.little-windows.com/blogs/faq/8303843-embedding-putting-stuff-in-resin
https://craftbits.com/project/basic-resin-casting/
https://www.little-windows.com/blogs/faq/8303843-embedding-putting-stuff-in-resin
https://youtu.be/Y0Wp9CmSKFY
https://www.youtube.com/watch?v=0153vh-vz_U
Lots more articles on making stained glass with resin, if you Google it. Good luck. It is very pretty.
Looks like Gallery Glass and glass beads. Easy, you can do this. Have fun. Best of luck.