Rev. Rul. 54-550

For the purposes of section 114(b)(4)(A)(iii) of the Internal Revenue Code of 1939, as amended by section 319 of the Revenue Act of 1951, and section 39.23(m)-5(a) of Regulations 118, a clay will be considered a "refractory and fire clay" if it has a pyrometric cone equivalent of 15 or higher. A clay having a pyrometric cone equivalent of less than 15 will not be considered a refractory or fire clay unless used or sold for recognized refractory purposes, such as (but not necessarily restricted to) ladle lining.