This material was posted on patreon by Foot of the Mountain Adventures
Some of the following are variations or expansions on rules found in OSRIC and/or AD&D manuals that I use in my own campaign.
A regular spell book weighs about 15 lbs and has an encumbrance of three times that much. In my game, they cost 750gp + 150 gp per level of the highest level spell written in them and can contain 40 levels of Magic-user or 20 levels of Illusionist spells (for example, 8 fifth level spells or 5 eighth level Magic-User spells.) These are a variation on the rules in Unearthed Arcana.
Traveling spell books weigh about 3 lbs and have an encumbrance of twice that. They cost 300 gp +150 gp per level of the highest spell written in them and can hold 10 levels of Magic-user or 5 levels of Illusionist spells.
Non-literate cultures will use alternate forms of spell books of equivalent costs and size. One such culture in my game uses intricately woven sculptures.
A Magic-user can read another Magic-user’s spellbook through the use of a Read Magic spell. Likewise, an Illusionist can read an Illusionist’s spellbook via a Read Illusionist Magic. A caster can learn a spell of appropriate class and level by reading another caster’s spell book. In my game, a caster can try to learn one spell per day (see also my post about starting, learning, and preparing spells.)
If a spellcaster is in utmost need, they can cast a spell from a spellbook as though it were a scroll. The caster can only cast a spell of the appropriate class, and one which they already know. Casting a spell from the book will destroy that spell. The caster should also roll a d100 – on a roll of 01 the entire book is consumed, on a 02-10 the spells on either side of the cast spell will also be consumed.
I treat spell books as scrolls to determine their value (either for awarding XP or determining the sale value.)
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