How to Use Object GrimoiresGrimoires come with instructions on how to use. Actually, thematically speaking, they are instructions on how to use. Which means that an object grimoire is going to be harder to use... at least until you know what its for and how to use it. Sure this bowl is enchanted... but does it control the winds, the waves, merely predict the weather, aid a comprehensive weather control spell, or aid something completely different like summon a delicious clam chowder?
Figuring out what a grimoire object does should be as interesting as translating a dead-language or encrypted grimoire. Hidden Lore and Research have a bigger role to play in doing so. In fact, most of the time, a Hidden Lore or Research role should be followed up by a Thaumatology roll. As a general rule, the Hidden Lore roll should be penalized, but be at +2 or more when compared with a plain research roll. Higher bonuses tend to be easier to find out about (research and hidden lore) but make the Thaumatology roll harder: a +1 amulet of inflicting diarrhea is hardly worth recording in the ancient books of lore, but isn't that hard to figure out, while a +8 change to frog statue is likely to be easy to find out about but hard to figure out the exact magical use.
Of course, these are all just suggestions. When purchasing such an item its likely the dealer will know exactly how to use it, or at least be able to point you in the right direction. This will probably effect the price of the item though!
Form and DecorationIf you're not going to get creative with the form of the item, there is little point in not leaving it as an arcane volume. Object grimoires usually are decorated with hints to their purpose and the form is part of the magic. Common forms include jewelry, decorated sticks (staffs, wands), statues, masks, bowls and tools. Its also common for such items to be made out of an expected material: a metal broom or a glass sword.
Pay attention to size. While the range of weights given in the RPM book are fine, some grimoire objects can be much bigger or smaller. Of particular interest is great big ones: you may be able to get a 7 foot iron statue grimoire for a great deal, but anytime you want to use it, you have to be at the statue.
Buying Object GrimoiresThese grimoires shouldn't cost the same as the standard "I-have-all-the-instructions" book. If the exact function isn't known, that's probably a discount (20%? 40%?). Great big ones will reduce the cost as well, and some GM's may say that the form is more conducive to that kind of magic, giving a bonus.
Of course, much of the time an object grimoire will be found when you're searching for a book. One way to use this is as ways to mix up the results of a grimore search. You can choose between the book in akkadian or the silver monkey necklace that puts an awkward 4 lbs hanging from your neck
Using Object GrimoiresThis is meant to help you mix up your grimoires, NOT to replace magic items in a campaign. These items still require a mage to use them, and the more powerful the caster, the more powerful the results. They are meant to shake up buying book after book, and to let some of that bizarre crap decorating the witch's shop actually be useful.
They're also very useful for magical traditions where writing isn't central. I actually came up with the idea when trying to work out a TL 3 society using RPM and relying heavily on grimoires. I hope you find this idea useful.