Abstract: An improvement is disclosed over conventional internal sizing of stock furnish for papermaking, wherein alum is added to the thick paper stock and the long retention time permits complete reaction with the fibers. The invention process permits successfully adding novel aluminum rosinate size composition unconventionally in thin stock furnish, where retention times are on the order of less that 1 minute. The highly charged aluminum rosinate size is able to be quickly adsorbed onto the fiber surfaces to permit surprisingly efficient sizing in thin stock. The quick sizing avoids concern with rising pH over time (in conventional thick stock application) and increases sizing efficiency.