A developer comprised of a toner and at least one external surface additive, wherein an acid-base interaction has an Interaction Surface Parameter (I.sub.SP) of greater than 0, and wherein I.sub.SP is defined by the following equation: [(K.sub.a).sub.toner.times.(K.sub.b).sub.additive]+[(K.sub.b).sub.toner.t- imes.(K.sub.a).sub.additive]-[(K.sub.a).sub.toner.times.(K.sub.a).sub.addi- tive]-[(K.sub.b).sub.toner.times.(K.sub.b).sub.additive], wherein K.sub.a is the Lewis acid value and K.sub.b is the Lewis base value.