Gregg Stewart said:
I used Danish oil on a Flamed Koa top to bring out the figure and then went over it with a wipe on poly urethane to keep the oil in the wood and off my clothes. Danish oil doesn't harden up. It did a nice job of making the flames pop though.
Danish oil can be many things. It can be a thinned polymerizing oil (such as Pure Tung or Linseed) or it can be faux product that is nothing but thinned polyurethane and or mineral spirits with waxes dissolved in them.
Notably on the last item, its common for the "popular" (famous, but low price) brands to be not much more than dissolved waxes. The spirits and or thinners carry the wax into the wood where they penetrate a bit, then the thinner evaporates and the wax is left behind. Coat after coat will give some gloss as the wax builds up. And of course, its easy to repair.
Polymerized oils WILL harden, but they harden slowly, and take a considerable amount of time to do so. For instance, Linseed oil may take months or years to fully cure, if thick. The idea with all oil finishes is to try and NOT build up any, wipe it thin as you can after the initial grain filling coat (wipe that too), Let all previous coats dry fully before adding more, because more will radically alter drying times, making them MUCH longer. It will cure eventually. Eventually being the word.
Thinned poly finishes have been passed off as "danish oils" and these are no different than poly finishes, except they have slow drying properties and are very thin, made to go on thin, and remain thin, and not build up.
By far the best - remains - pure tung oil, found at wood specialty shops (not Home Depot or Lowes)