The term “Rainbow Poplar” does not refer to a separate wood species, but rather, is a designation of Yellow Poplar that has been mineral stained. Rainbow Poplar exhibits a variety of colors ranging from green, purple, black, red, etc. It is this distinct variety of colors that turns an otherwise oridnary piece of Poplar into the intriguing Rainbow Poplar. The precise cause of these streaks and discolored wood produced in certain trees is not fully understood. Poplar is very easy to work in almost all regards, but one of Poplar’s only downsides is its softness. Due to its low density, Poplar can sometimes leave fuzzy surfaces and edges: especially during shaping or sanding. Sanding to finer grits of sandpaper may be necessary to obtain a smooth surface. 3" x 3" x 12" Spindle Turning Blank.