The grades of rosin shall be designated, from highest to lowest, by the following letters, respectively: XC, XB, XA, X, WW, WG, N, M, K, I, H, G, F, E, D, B. In addition, the letters OP shall be used to designate the grade of opaque rosin, and the letters FF shall be used to designate the grade of normal wood rosin: Provided, That the product recovered in the refining of wood rosin, that is darker in color than the standard for FF grade, and that contains rosin acids in lesser quantity than is normal for such rosin, shall be graded and designated as B wood resin.

[11 FR 14665, Dec. 27, 1946, as amended at 17 FR 221, Jan. 9, 1952; 33 FR 8722, June 14, 1968]