African Blackwood, Desert Ironwood, Kingwood, Cocobolo, or most other woods that do not have at least some slight porosity. For a lack of a better way to say it, Tru-Oil should be used only on those woods where the base coat can "soak" in a little bit and give the remaining coats something to "grip". Apply Tru-Oil to woods that don't present that characteristic means it will either not dry, or if it does it will easily "peel".