Study › Runes & Norse › The Blank Rune

Many rune sets come with a 25th, blank rune. It is not an ancient rune: it first appears in Ralph Blum's The Book of Runes of 1982.
What is the blank rune?
Many modern rune sets come with a 25th stone that has no rune on it, the blank rune. It is not an ancient rune.
It first appears in Ralph Blum's The Book of Runes (1982), which was sold with a small bag of rune tiles and did much to make rune casting popular. Blum's own set, he wrote, already held a blank tile, most likely a spare; he gave it a place, with no basis in history or tradition, called it Odin's rune, the rune of "the unknowable", and set the runes in an order of his own.
No runic inscription, no eddic poem and no saga knows of a blank rune. A row of runes was an alphabet, and an alphabet has no empty letter. Serious rune practitioners do not use the blank rune in their divination, and this app uses the 24 runes of the Elder Futhark alone.
The 24 runes are listed in the order of the runes, starting with Fehu.
Questions
Is the blank rune real?
No. No inscription, poem or saga knows it; it comes from a book of 1982.
How many runes are there?
The Elder Futhark has 24.