The Blank Lexicon is a miscellaneous item given to the Dragonborn by Septimus Signus during the quest "Discerning the Transmundane." It can be used to unlock access to the Elder Scroll and progress the quest.
It must be given to Septimus Signus in order to retrieve the Oghma Infinium. The Blank Lexicon will turn into a Runed Lexicon after it is used to unlock the Elder Scroll's container during the quest "Discerning the Transmundane."
- If it is taken back from Septimus' corpse, it may get stuck in the inventory, listed as a quest item. The same can apply to the Essence Extractor as well.