The "test" is quick and dirty, one application of tannic acid followed by the iron solution. For finishing the the tannic acid would require several applications before the iron solution but I have an idea of how the ebonising would work on different woods.
White Oak responded as expected, the Cherry was a surprise how well it worked. The South American Walnut was pretty much as expected, it will go almost black with just oil. Poplar might work better with additional applications of tannic acid prior to the iron and the same would apply to the Red Oak but as tested they were both disappointing.