The Barddas of Iolo Morganwg, Vol. I., ed. by J. Williams Ab Ithel, , at sacred-texts.com
The Peithyn Coelbren consists of staves placed regularly together in a frame.
p. 158 p. 159
The palm Coelbren consists of small squares of wood of the shape and size of dice, each containing a letter, and a small hole, through which a string is passed. There are as many strings as there are letters; that is, is lettered on one string, on another string, and in the same way with every string, each string having its own letter. And where knowledge is mutually communicated in secret, one man takes from his string what is necessary, and the other answers him back in the same manner; and thus from palm to palm as long as is required. This is called the palm Coelbren, and the palm speech, and the palm alphabet; and frequently has vocal song been lettered in this way, that is, the first verse on its own string, the second accordingly, and all the following verses to the end of the song. And between word and word, in order that each word might be distinctly evident, a round piece of wood is inserted. This is called the dumb Coelbren, and the dumb alphabet; and it is called the imparting of secrets, for it can be done in sight of all the world, without any body knowing it, except the privy friends alone.
157:1 p. 156 Peithyn, any thing ribbed or cogged, a term applied to the Wooden Book of the Bards.