a method of making an identifiable article such as a container or container preform . a molded plastic container or container preform is provided that includes a wall having at least one layer of matrix resin and at least one layer of barrier resin that is blended with an additive . the wall has at least one localized portion of predetermined geometry in which the barrier layer is thicker than surrounding portions of the wall , and within which the additive is discernable under visible or uv light so as to provide a means to prevent use of counterfeit containers .