Something Medieval?

Page of medieval, ecclesiatical music with words in Latin
Music Manuscript Page: Side 1

I have recently been given a large sheet of paper with music on both side and Latin words. It looks really old, but I don’t really know much about it at all. I know it isn’t what wwe usually think of as archaeology, but perhaps some YAC members might be interested in doing some research about it?

Here is what I know. The page was bought by my father-in-law from a bookseller in Dublin in the 1950’s. Apparently the seller was pulling pages from a large book and selling them for so many shillings each to customers. There is a bad tear and several scissor or knife cuts. The page is vellum; stretched, dried animal skin. It was used to make good quality and long-lasting paper for many centuries.

The first side has what may be a page number in the top right: XXVI, Roman numerals for 26. Curiously there are no musical notes on the first line (stave), but it is possible to see very faint writing immediately below. It looks as though it has been painted out with something. Perhaps the copyist made a mistake? A piece of vellum was probably too expensive just to throw away, so the mistake was covered up and the copyist started again.

Page of medieval, ecclesiatical music with words in Latin
Music Manuscript Page: Side 2

The reverse of the page is noticably darker. I wonder why? Is this normal with vellum perhaps? There seems to be a circular stain in the top right of the page, perhaps from a coffee cup?

There is also some modern writing in pencil in the middle of the margin on the left. The firtst line seems to read 35/68 but I’m not sure about the four letters or numbers beneath.

So; questions. How old is the sheet? Where is it from? What was the music for and who sang it? How does one look after old vellum? Is there any way to find out what the first line of the text says?

Anyone interested in helping to find out more can let me know.