unvulcanised natural or synthetic rubber, compounded before or after coagulation either with carbon black or with silica, a mix consisting of elastomer and generally only one other ingredient, the proportion of which is much higher than will be present in the final production mix. Masterbatches are used for cleanliness, , masterbatch, base compound - a quantity of material to which pigments and extenders are added at an early stage of manufacture and which assists in obtaining uniform mixtures