Wikipedia has a direct description of the origin of this expression. “The phrase “span-new” meant as new as a freshly cut wood chip, such as those once used to make spoons. In a metaphor dating from at least 1300, something span-new was neat and unstained.” Spick was added in the 16^th century and may have evolved from the Dutch words spiksplinter nieuw, meaning “spike-splinter new.” The use of the expression became commonly used to indicate something is completely clean when the household cleaner “Spic and Span” was put on the market in the 1920s.