Ralph Hull marketed a three-knife set as “The Juggling Knives”, 1935 (see The Linking Ring, Vol. 15 no. 10, inside front cover), but did not seem to claim to have been the first to adopt the ancient Paddle Trick to pen knives (although a common knife was one of the earliest props used for a Paddle Trick; see J. Prévost's La Premiere Partie des subtiles et plaisantes inventions, 1584, p. 16, for the English translation see Clever and Pleasant Inventions, Part One, 1998, p. 30). In Hull's routine, only two knives were evident, one white and one black. This routine is the basis for what became the classic two-knife routine in which the knives transpose.
John Stanfield is usually credited with the Slow-Motion Color-Changing Knife, marketed as “The Colorfusing Knife”, 1952: one side divided into two colors, roughly one-third and two-thirds of the length. However, in The Linking Ring, Vol. 37 No. 8, Oct. 1957, p. 78, Gene Grant claims to have come up with almost the same idea (the difference being that the split side is divided at the center) “long before Stanfield put his Colorfusing Knife on the market.” To further confuse the issue, in Abracadabra, Vol. 74 No. 1903, July 17 1982, p. 106, William Zavis claims that the one-third/two-third split side was a feature in Walter Jeans's original knife routine. Zavis may have drawn this information from an article by Alex Elmsley, “Jeans Chameleon Knife”, published in My Best Close-up Trick, edited by Harry Baron, 1954, p. 24. There it is stated, “Alexander Elmsley invented this colour changing penknife about four years ago. Since then he has discovered that many other people 'invented' it before he did, and the earliest he can find is Walter Jeans.” However, twenty years later, when the trick was reprinted in New Pentagram, Vol. 6 No. 4, June 1974, p. 27, this line was added by Peter Warlock: “Later he found [that Walter Jeans had preceded him], though he is now unable to state the source, and for that matter despite the very big file that we have on Walter Jeans, we have no record either.” The matter remained unresolved, as the Color-Changing Knife is not mentioned in Warlock's 1986 book, Walter Jeans: Illusioneer. Unless further information turns up, this attribution must remain in question.