[footfootfoot]

Here's the cliff notes on varnish.

Varnish is made from oil and resin and is thinned with some type of solvent. The more resin a vanish has (relative to oil) the harder it will be, and the more oil it has (relative to resin) the softer it will be.

Softer varnishes are often called "Long oil varnishes" and are used primarily outdoors or in marine applications where the wood is subjected to extremes of temperature and moisture. The relative flexibility of a long oil varnish allows it expand and contract without cracking.

Harder varnishes are called "short oil" varnishes and are used for things like musical instruments and furniture. The higher resin content makes the varnish resistant to dings and scratches and wears well but will not tolerate extremes in movement through temperature and humidity chnages as well as a long oil varnish.

Short oil varnish, because it is so hard can be rubbed with pumice or steel wool to dull the sheen and give a satin or matte finish, it can also be polished to create a high gloss. Long oil varnish, because it is so soft and flexible, cannot be rubbed out or dulled with steel wool satisfactorily. Some varnishes have talc added to make them matte, These should be avoided because the talc reduces the strength of the varnish.

Exterior varnishes are sometimes called "spar varnish" Anything you buy in a hardware store that is called spar varnish is crap and will not last very long before it starts cracking and lifting off the wood. To get real spar varnish you need to go to a marine specialty store and expect to pay at least $35 a quart.

Polyuethane varnishes are particularly shitty IMO, especially compared to real varnish.

Good brands are Behlen and Epifanes. Behlen makes a wide range of varnishes, Epifanes is known for marine varnishes.

There are entire books about varnishes.

ETA: Cutting boards.
Never use vegetable oil on a cutting board; the oil won't dry and it will get rancid and gummy. If you feel the need to oil a cutting board (they don't need that, btw) use mineral oil or walnut oil. Walnut oil will actually dry, unlike vegetable oil. Mineral oil will not dry, but it won't t go rancid.