World Rules of Carom BilliardArchived 2007-09-28 at the Wayback Machine (English language version), Chapter II ("Equipment"), Article 12 ("Balls, Chalk"), Section 2; Union Mondiale de Billard, Sint-Martens-Latem, Belgium, 1 January 1989 (official online PDF scan, accessed 5 March 2007).
World Rules of Carom BilliardArchived 2007-09-28 at the Wayback Machine (English language version), Chapter II ("Equipment"), Article 12 ("Balls, Chalk"), Section 2; Union Mondiale de Billard, Sint-Martens-Latem, Belgium, 1 January 1989 (official online PDF scan, accessed 5 March 2007).