Liber Florum
The would-be reader of the Liber Florum is well advised to not touch any copy of this book with their bare hands. This includes modern facsimiles, although it’s apparently safe enough to handle individual pages that have not been not bound in any way, up to and including sheet protectors in a three-ring binder. That’s how people know that the book is magical, by the way. And apparently actively malevolent.
The text is 17th Century, Neo-Latin, probably Saxon in origin: the Liber Florum was probably written during the the witch-hunting craze (somewhere around 1655-1660 is tentatively agreed upon by scholars). Interestingly, it seems to have been written under the assumptions that: evil witches actually did exist; both Catholic and Protestant witch-burners were in fact finding and killing witches; and it was the unholy duty of what witches that remained to create nature-infused agents of retribution to strike at the hated servants of the White Christ, wherever they might be found. This last part was not made clear until the end, when it was revealed that the act of reading the Liber Florum was itself a magic spell for transforming the reader into such an agent. Although ‘curse,’ obviously, might be a better term.
And that’s why the need for gloves. The original texts were copied and burned in the 19th Century, obviously; and while the reproductions do still have a certain amount of inherent malevolent power to them, that power has been drastically attenuated. At this point the major effects from reading the Liber Florum with bare hands seems to be the granting of a green thumb for growing poisonous plants, and a tendency to snarl at Christian clergy at the slightest provocation, or none. Unfortunately, this is deemed a reasonable potential price to pay for having access to a tome that has proved invaluable for centuries when it comes to analyzing and countering Diabolical plant-themed magic. Besides, the effects fade over time. Eventually.
One last note: more than one modern neo-pagan researcher and/or cleric has come across the Liber Florum, gotten understandably upset at its nature and implications (for the record; this book seems to have no influence on the Gardnerian version of Wicca), and set about trying to ‘cleanse’ the text. Some have even managed to survive the attempt. The ones that do invariably then decide to just let the Christians deal with this one.