This is something long overdue. We don't have any recording media with a life span more then a few decades at best.
The horror stories of old films and magnetic tape recordings has been told over and over.
I personally experienced trying to recover data off 9 track tape and having the glue get gummy and the take stick to the recording head.
Even CD's and blue ray don't have much of a life span.
Any long term medium should be non-conductive, to protect against EMP.
UV resistant so not degrade in sun light,
Survive temperature extremes.
Be mechanically sturdy so it doesn't break
Resistant to long term water / moisture and microbial growth.
Resistant to long term exposure to low intensity radiation. (natural background, and radon and other sources)
Plastics and other hydrocarbons like epoxy absorb moisture and break down with UV and microbial action.
Even Glass may possibly deform over 100's of years as it's a semi-liquid.
This leaves only a few things that could work.
Silicon Carbide, Diamond and other hard crystals are probably the best bet.
Maybe graphene, nanotubes or other carbon forms.