I just wanted to put this out there so that aspiring rune workers can learn from this bit. The blank rune holds no place in traditional rune work. It was never a stav that was considered to be worked with. So when you get a rune set online or from a store don't use the rune and don't discard it. Simply keep it in case one of your rune stones break.
The whole blank rune idea started largely with Ralph Blum. This author began selling his book with premade rune sets in the 80s. I have one of the original sets and the original book. I can honestly say that Blum's book is sound but it contains ideas that are not traditional and are largely New Age concepts pulled from cultures from various parts of the world.
If you do not value the tradition a whole lot then by all means use the blank rune. It's up to you, I can't force you not to. Just know that it really isn't a rune at all. Just a blank stone or piece of wood.