Reply by Arminius

It is basically an oil/varnish blend, with some properties of both, usually wiped on. Key concept is that it both penetrates and builds up a finish – though the ‘build’ is minimal, it can barely be felt. The oil can be a linseed or tung oil base. The drying oil component of the varnish (resin + solvent +drying oil) is usually something with the same base- I am not aware of a Danish oil blend that has polyurethane, though it is probably possible.

Woodwrecker is getting similar results because it is not that different in effect.