Spell books

This is a page from an alchemical manuscript in the Getty collection, and it's a pretty good fit for how I imagine the instructions for casting spells to be written out in spell books in my campaign.

There's no explicit "Tak ye ane silvere bowle by Midnyte ynde fille it with ye Teares of Ane Pure Mayde..." sort of instructions here.

The numerical sequences would have relevance only to whoever it was who wrote them down, or to someone who had deciphered his or her unique system of notation.

The images might be literal renderings of how material spell components must be laid out, or perhaps they're just mnemonic aids to achieve a particular mental state. Or maybe both. Again, unless you know the specific system used by the original writer, having access to the page itself would be of limited usefulness.

As you can imagine, copying out a spell description like this would take plenty of time, concentration, patience and skill, and certainly wouldn't be the sort of task one would want to undertake in the primitive conditions of your average monster-infested dungeon.

So until you've managed to decipher the systems of notation and illustration as used by the person whose book you've just stolen acquired found, it's not going to be of a great deal of use to you. It's still valuable though, so don't lose it.