A method as in claim 1 wherein: the carbon black is present in the extrudable mixture in an amount from about 10 to about 70 parts, by weight; the ceramic forming material comprises ball clay present in the extrudable mixture in an amount from about 20 to about 80 parts, by weight; the flux is a feldspathic mineral present in the extrudable mixture in an amount from about 2 to about 20 parts, by w