A thermal processor including a rotatable hollow drum including a drum core having an interior surface and an exterior surface, and a radiant heater positioned within an interior of the drum and configured to provide radiant energy to heat the drum, wherein at least one radiant energy absorption characteristic of the interior of the drum varies across its longitudinal width Wd so that selected areas of the interior of the drum absorb more radiant energy than other areas of the interior of the drum so as to compensate for non-uniform heat loss from the drum and to provide the exterior surface of the drum core at a desired temperature which is substantially uniform across the longitudinal width of the drum core.