  We study stable commutator length (scl) in free products via surface maps
into a wedge of spaces. We prove that scl is piecewise rational linear if it
vanishes on each factor of the free product, generalizing the main result in
Danny Calegari's paper "Scl, sails and surgery". We further prove that the
property of isometric embedding with respect to scl is preserved under taking
free products. The method of proof gives a way to compute scl in free products
which lets us generalize and derive in a new way several well-known formulas.
Finally we show independently and in a new approach that scl in free products
of cyclic groups behaves in a piecewise quasi-rational way when the word is
fixed but the orders of factors vary, previously proved by Timothy Susse,
settling a conjecture of Alden Walker.
