A player asked me if he can write a spell in his blessed spellbook and then rip off the page to use it as a scroll.
For a wizard to scribe a level 3 spell (say, Fireball) into his spellbook takes 3 hours, uses up 3 pages, and costs him 90 gp in materials and costs.
If he has another spellbook with that spell already in it, and he's just copying the spell into a new spellbook, it costs half that.
In order for that same wizard to make a scroll of Fireball, it requires 1 day of work, expends the spell from his spells for that day, and costs him 187.5 gp. Assuming he has the Scribe Scroll feat.
So you can see that for about 45.45 gold, he can copy a Fireball spell into a new spellbook. Ripping out the page saves him 5 hours, the prepared spell slot, and 142 gold.
Assuming that you do not allow it to work with a normal spellbook, but only a Blessed Book, and that he created it himself, that's 6.25 gold per page. so the cost of scribing a Fireball into the Blessed Book becomes 63.75 gold (45+(6.25 x 3 pages)). Ripping the page instead of scribing the scroll still saves him over 123 gold. (If he is forced to buy the Blessed Book instead of creating it, he still saves 105 gold)
And the savings go completely crazy when you have expensive material components, like Khrysaor says.
No. Just no. Totally illegal, and for good reason too.
If you could do this no one would ever buy scrolls since scribing spells into a spellbook is cheaper and faster than scribing an actual scroll. This is even more cheesy with a blessed book, as there is nothing stopping the scriber from scribing a spell into the book FOR FREE, ripping it out to cast it like a scroll, and then re-scribing the same spell. Essentially, he'd have 1,000 free scrolls for the low cost of 6,500 gp. What's more he'd be able to scribe high level spells quicker (scrolls take 2 hours or a day or more, scribing into a spellbook only ever takes hours).
This is not only cheesy and broken, it's illegal.
No. Just no. Totally illegal, and for good reason too.
If you could do this no one would ever buy scrolls since scribing spells into a spellbook is cheaper and faster than scribing an actual scroll. This is even more cheesy with a blessed book, as there is nothing stopping the scriber from scribing a spell into the book FOR FREE, ripping it out to cast it like a scroll, and then re-scribing the same spell. Essentially, he'd have 1,000 free scrolls for the low cost of 6,500 gp. What's more he'd be able to scribe high level spells quicker (scrolls take 2 hours or a day or more, scribing into a spellbook only ever takes hours).
This is not only cheesy and broken, it's illegal.
Somewhere around level 15 the PC would be thinking, you said we took how long off of the adventuring? 1 month bwahahaha. If you'll excuse me I have some craft checks to make. 5 craft checks. I'm never worrying about spell casting limits again. Woot.