Simulation methods are used to explore the potential for temper to confound the source attribution of chemically characterized archaeological ceramics. Addition of a given temper to two clay source-related compositional groups draws these groups together in compositional space, eventually fusing them into one group as the two mixtures approach pure temper. Although progressive coalescence of the group centroids eventually causes the groups to overlap, addition of sizeable amounts of temper may be required before any significant overlap occurs and before the stage of unresolvable overlap is reached. The tendency for groups to coalesce as temper is added is greater for more heterogeneous tempers. Overlap between tempered groups also depends on the degree of initial separation between the untempered clays and on the relationship between the composition of the clays and temper. -- AATA