Mavesyn, your memory may have failed you here.
Shellac is basically a wood varnish that is made up from crystals mixed with methylated spirits. Track riders (especially sprinters) used to apply this to tubular rims in the 1960/1970 era.
This was a lengthy process where about 3-4 coats were applied to the rim and 2-3 coats to the cotton cloth at the base of the tubular tyre.
Each coat had to dry before the next and when complete, a final coat was put on the rim and the tub fitted, seated and pumped up.
Fitting this correctly made it almost impossible to roll the tub on any banking, even with Chris Hoy-type power (but of course, in those days, it would be Pierre Trentin or Daniel Morelon).
TBH, I've never heard of it being applied to handlebar tape. It would crack, slip and look revolting, as it was a mid/dark brown when applied.
Old enough to know better!