The melting point of organic material is significantly lower than the melting point of even the coolest glass' melting point. You can't encase organic material in glass. Even the ambient temperature inside the core, assuming a hollow core, is too hot for the organic material. If the core was solid, the organic material would burn up quickly. Artiest have tried over the centuries to encase organic material with no success. Buyer beware if the person claims the material inside is organic in nature....lol.
Encasing in plastic is a totally different animal - of course, it certainly can be done!