The Barddas of Iolo Morganwg, Vol. I., ed. by J. Williams Ab Ithel, , at sacred-texts.com
The three principal materials of knowledge of the Bards of the Isle of Britain: wood, that is Coelbren; and Coelvain; which two existed before the faith in Christ was obtained; and when that was obtained, knowledge and understanding was had of the third, namely Plagawd, that is, the dressed skin of a beast, which is called parchment. (Grawen. 1 There are two grawens: one of wood, the other of a beast.)
163:1 It is not very clear whether this word is the same or not with crawen, a crust, having here the meaning of rind or skin.