I've found some literature that says shellac sealing properties vary
based on age and at the best of times it's not a 100% barrier at all.
But still better than nothing.

I'm in the process of ordering activated carbon for my ventilation
system, which I'm building with overkill in mind.

I use acrylic paint, also work with plaster, latex, gelatin, various
stones, watercolors. I don't think artist's acrylics are a good sealer
though and pretty expensive for furniture.

I'm wondering about the toxicity of PVA glue... they say children's
glue is non-toxic... is it not really? Why not just thin it down and
apply it heavily over everything?