The nail writer is an extremely powerful tool for the mentalist. It's origin is unclear. One of the earliest references can be found in the book Spirit Slate Writing and Kindred Phenomena, written by William. E. Robinson and published in 1898. Therein it was called "The Thumb Pencil Carrier". This booklet will give you an easy start using this gimmick.
We have had a high opinion of the "nail-writer" ever since, a good many years ago, Paul Rosini gave us a demonstration in which he used this tiny piece of apparatus. Of course, it does not follow that, just because Mr. Rosini produces a near-miracle with the aid of this "fake," all magicians can employ it with equal success. Indeed, no branch of conjuring demands a higher order of showmanship than the field of "psychic phenomena," where the nail-writer finds its largest usefulness. But it is likewise true that few feats of magic are so amazing to the average beholder as those in which the performer apparently plumbs the depths of a spectator's mind or predicts in advance the particular word, number, name, playing card, or other mental image upon which his "subject" is about to concentrate.
Twelve of the tricks explained here are in the nature of predictions. In five, the performer predicts the names of cards that will be drawn; in two, numbers that will be written down; and in yet others, one or more words, a throw of the dice, the amount of money in the possession of anyone whom a spectator may choose to call by telephone, the musical selection a spectator will play or sing, and other tests of prevision. It will be noted that there is a family likeness about these 12 tricks, as is almost inevitable in feats of this kind. There are, to be sure, differences in the precise methods employed; but the broad effect is always the same, and the nail-writer is used in all instances. One of these tricks, we regret to report, requires confederacy, which places it outside the pale of legitimate conjuring, despite the recommendation of its originator and regardless of whether the author (or the editor) is or is not correct in believing that "your stooge" will never be suspected!
Of the nine other tricks in Twenty Stunners with a Nail Writer, five are feats in which the performer's assistant names a card that was removed from the pack in his absence, finds in the pack a card named while he was in another room, discovers a magazine advertisement under similar circumstances, and does essentially the same thing in two slightly different book tests. There are two feats in which the performer reproduces (once on a slate, and once on a blank card) words, figures, or names written by spectators. Making up the total are an old (and not very good) item taken from William E. Robinson's Spirit Slate-Writing, and a "Living and Dead" test.
The text begins on page 7 and continues to page 25, making 19 pages of explanatory material in all. Five of these describe, with diagrams, several types of nail-writers, and explain how to use them; the remaining 14 pages of actual text deal with specific tricks. We may note, finally, two pages of introduction by Ralph W. Read, and a half-dozen filled with advertisements. The pamphlet is neatly bound in soft boards.