Here's something I just learned about illusionists in 1st edition that doesn't sit quite right with me: they don't have to use read magic to read illusionist spells in books and scrolls. According to the AD&D1 DMG, illusion spells are written in a secret tongue taught to all illusionists during their apprenticeship.
I never knew this because, in my entire gaming history, nobody I've ever played with has rolled up an illusionist, and I'm pretty sure that specialist wizards in AD&D2 all work exactly like normal mages when it comes to read magic. (2nd edition illusionists included)
For some reason, this little tidbit just doesn't jive with me. (Of course, maybe that's why the minimum starting age for an illusionist is 31 years old vs. magic-user's 26)
I also find that the concept is somewhat contradicted in the DMG's section on scrolls, where all scrolls aside from protection-type scrolls require a read magic spell to decipher.
That leads me to scrolls in general: all scrolls require read magic to decipher except for protection scrolls (which can be read by any character). How is it that classes without access to read magic would be able to create scrolls that can be read by no other means?
A final nitpick on magical writings is that rangers can eventually learn to cast druidic and magic-user spells, but cannot read them from scrolls. Likewise, the thief cannot cast spells, but may read magical scrolls. I suppose the partial education of those classes is sufficient to at least hand-wave the matter.
Since I anticipate tinkering quite a bit with AD&D, I intend to address the issue of magical writing and the use of read magic. My initial idea is thus:
Magic-users will have a secret set of written language much like illusionists do. This allows them to decipher magical scrolls and writings, but only up to the level they can cast. A 3rd level magic-user who finds a scroll with web can read the scroll without magical aid, but he cannot comprehend a spell with fireball on it because his understanding of magical writings is insufficient to comprehend a 3rd level spell. The old read magic spell becomes something of a translator-type spell: the magic-user can use it to reveal the nature of spells beyond his comprehension. He could then read scrolls or even copy a higher level spell into his spellbook, although he'd still be unable to memorize it until he reached the proper level. Read magic would also allow him to determine the nature of an illusionist, clerical, or druidic scroll, including what spell it is, though of course he would still be unable to use it.
Druidic spells would be written in the druidic language. Characters who have somehow managed to learn that secret tongue (an assassin, for instance) would be unable to cast the spell regardless because they have no connection to the powers of nature.
Clerical scrolls are written in a church dialect that all clerics learn during their seminary, something akin to Latin in the medieval church. While non-clerical religious scholars or curious academics might be able to learn this language, they lack to training to connect to the divine and thus the scroll can't be employed as a spell.
Illusionist spells will remain written in the secret illusionist language, readable and usable only by illusionist characters.
An additional rule I am contemplating is that the reverse of read magic, undetectable magic, be made permanent in duration, or perhaps it lasts one year per level or is particularly long lived. It renders magical writing unreadable until read magic is employed.
It occurs to me that the format of a spell is most likely different on a scroll than it is in a spellbook: the writing is charged with energy and I see it as a sort of "magical shorthand." (For magic-user and illusionist scrolls, that is...the idea isn't applicable to clerics and druids as they lack spellbooks.) Magic-users and illusionist still have to make a "chance to learn spell" roll if they desire to copy the scroll into their book, because they have to essentially reverse engineer the true version of the spell from the magical shorthand. For copying a spell of higher level than what one can cast, I would impose a penalty of -10% per level difference.
The spell comprehend languages cannot be used to decipher a magic-user or illusionist scroll, as I see those languages as more of a system of mathematics or scientific formula than I do an actual language that one could communicate in.
I think we've got ourselves a workable system, folks.