They make a waterproof product for shoes, boots, tents etc.
This link I found by doing a Google search.
https://www.tripsavvy.com/best-water...sprays-4773587
Since this is a piece of art you want to save. I would do research and not try the first thing you come across. I myself have ruined a project or two by not taking my time to find the correct or right solution to my preserve a project.
Use a "test" fabric similar to the piece you want to waterproof and watch the results.