The slate was found on the island at Tintagel in 1998. I believe it reads
The Tintagel slate (Glasgow University)
- MAV E[IGIR]
- COLI AVI FICIT
- COLI [AVI]
where the bracketed letters are now missing and some of the words run together. A cross occupies the space between lines one and three.
The letters in the first line are in larger characters. They are not easy to identify and their interpretation has changed since the slate’s discovery. The M and A are ligatured with the start of the letter M being only just visible. The text below the cross occupies five lines and the script is smaller. The lefthand diagonal descender of the letter V in the third line is just about visible. Also, what has thus far been interpreted as a G on the fifth line is in reality an R and G ligatured as illustrated below.
Letters r and g ligatured
That the horizontal stroke of the ligatured letter R is not a scratch mark is indicated by its in situ image and its reconstruction diagram:
Barrowman, R.C., Batey, C.E., Morris, C.D., 122. Photograph K.J. Brady.
Barrowman, R.C., Batey, C. E., Morris, C.D. (eds.), 2007. 193. Drawing McEwan, L., Thomas, A.C. after Thorpe, C.
The inscription is clearly Arthurian as indicated by the following interpretation. The text in lines one to four form a sentence which is repeated in lines five to seven, but with the matronymic missing and the name Paternus replaced by Artorgnou. This suggests that they are alternative names for the same individual. The slate thus reads:
The son of Eigr, Paternus, made this for Coliavus.
The renowned Artor made this for Coliavus.
Charles Thomas wrote:
“Line (ii), which is complete, shows a name in latinized second-declension genitive – Coliauus, as Coliaui – followed by a verb, for which the preceding name ought to form the subject. This is not a Roman name. It comprises an element Col-, concievably the same as Coll-, meaning uncertain, found in Celtic name-formation; for example, an Irish ogam inscription with 117 COLLOS (Co Cork). This has been extended with a known British hypocoristic or ‘pet-name’ ending, -iau, in a written Latin context presented as -iauus (the first ‘u’ is a /w/sound).” So Coliauus can be identified with Coll.”
The individual, Coliavus, is listed in the Llyfr Baglan as being one generation earlier than Arthur, see Coliavus.
We thus have an inscription with an interesting mix of Brythonic and Latin text. HG 2 states the father of Arthur was Petr. ByS 21 says the father of Padarn was Pedrwn. So, Arthur and Paternus had fathers of the same name, Petranus, supporting the proposition that the two names refer to a single individual.
 Barrowman, R. C., Batey, C. E., Morris, C. D., 2007, 199.