N.C. Gen. Stat. § 105-277.10

Precious metals, including rhodium and platinum, used or held for use directly in manufacturing or processing by a manufacturer as part of industrial machinery is designated a special class of property under Article V, Sec. 2(2) of the North Carolina Constitution and shall be assessed for taxation in accordance with this section. The classified property shall be assessed at the lower of its true value or the manufacturer's original cost less depreciation. The original cost of the classified property shall be adjusted by the index factor, if any, that applies in assessing the industrial machinery with which the property is used, and the depreciable life of the classified property shall be the life assigned to the industrial machinery with which the property is used. The residual value of the classified property may not exceed twenty-five percent (25%) of the manufacturer's original cost.