Going back to Acorn4's comment regarding sanding laquer off, Ian MacDonald in is his excellent book Revolution In The Head, comments that:

"Lennon bought his own [Epiphone Casino] in 1966. In 1968, he stripped the instrument of its veneer on the then-vogueish assumption that this would improve its resonance; the fact that the unvarnished wood also gave it a look of deglamourised frankness presumably had its appeal."