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Opacity:
A state of non-transparency or translucence. The inability to see the support material under the pigment, for example parchment. The level of opacity is represented by the amount of pigment coverage.
Ottonian:
The Ottonian dynasty was ruled by the Saxons, a Germanic people who conquered the East Frankish (present day Austria, Bavaria, and Germany) portion of the Carolingian Empire from 919 to 1024. The Ottonian court was active in advancing the production of manuscripts, with monastic scriptoria.
Overwriting:
Writing on top of previous writing, as is the case with palimpsests.
Oxidation:
A chemical reaction resulting from exposure to oxygen. This can cause certain metal-based pigments to fade and/or turn a silver-black and to bleed. The conditions in which a manuscript is stored and the length of exposure to adverse atmospheric conditions determine the extent of oxidation.