The thicker and harder the finish, the more protection it offers to the guitar. Gloss or varnish finishes tend to be thickest, followed by nitrocellulose and French polish (along with Steve Toon’s oil varnish). Oil offers the thinnest layer of protection.

A gloss finish is also a hard finish, along with nitrocellulose (once it has fully cured). It therefore offers protection in this way too, by deflecting any impacts that may scratch or dent the guitar. Although nitrocellulose is also a hard finish once fully cured, the point of this finish is that it can be applied thinly, so the protective qualities are not as strong as a gloss/varnish finish. French polish and oil finishes do not set as a hardened surface on top of the wood. They simply act as a sealant to stop moisture interfering with the wood and offer some level of protection against scratches.