When loading the batch into the mixer, add pigments in the center of the batch, sandwiched between the polymers or slab.Adding them before the rubber will coat the chamber and may cause the batch to slip, increasing chance of some loose pigment.Adding them after the rubber may cause some of the pigment to be sucked up the dust collector as the ram comes down on top of the pigment bag and may cause some contamination of other mixes due to pigment adhering to the ram weight.