Worth mentioning also: Nick Lenz stated in his book that vaseline applications should be covered with tin a layer of tin foil to hwlp keep the callous flat. I would imagine it also helps prevent it from rubbing off or making a mess.
He also made an interesting remark about deciduous species. From the second edition of Bonsai from the Wild:
"On deciduous trees, especially maples and azaleas, Preparation H or a generic facsimile, the grease you rub on your butt or cracked hands, is preferred. One or more of the unknown ingredients greatly accelerates healing, especially when a thin smear is covered by with duct sealant*. Preparation H seems to offer no enhancement over petroleum jelly on conifers and is more costly. Beware of new formulations of hemorrhoidal ointments, such as lotions, mists, creams, and essences - only the greasy stuff works. Be sure to smooth all pruning scars with a sharp knife. The callous will cover with greater ease and flatness."
*Nick preferred this to more-expensive bonsai cut paste or putty.
Anyone tried this?