Cue sports playing nine-ball. Snooker balls are smaller than American-style pool balls with a diameter of 52.5 mm ( in), and come in sets of 22 (15 reds, 6 "", and a cue ball). English billiard balls are the same size as snooker balls and come in sets of three balls (two cue balls and a red, an object ball). Other games, such as bumper pool, have custom ball sets. Billiard balls have been made from many different materials since the start of the game, including clay, bakelite, celluloid, crystallite, ivory, plastic, steel and wood. The dominant material from 1627 until the
The Seven Crystal Balls adventures, which had actually been authored later than "The Seven Crystal Balls", in the English version, references are made to events that would occur in "The Calculus Affair" and "The Red Sea Sharks". Biographer Benoît Peeters described "The Seven Crystal Balls" as "the most terrifying of "The Adventures of Tintin"". He believed that in this story, Hergé had come under the clear influence of Jacobs, in that the "décor grows more lush; the details clearer. No more streets suggested by a few lines, monochromatic posters, or characters walking on the edge of the frame." Elsewhere, he noted that in this