The Faddan More Psalter was discovered in a peat bank in Tipperary in 2006. Written around 800 AD, it was deposited in a bog within 200 years of its making.
The text was written on vellum; a parchment made of uncured calfskin, and so gradually over hundreds of years the vellum slowly dissolved to glue. The mineral ink with which the text was written had somehow managed to preserve the vellum on which it was written. As a result the little fragments of text have freed themselves from the parchment that once bound them.
The information above is from a presentation on Celtic art by Dr. Katherine Forsyth at CCA Glasgow, 11/10/13