Scroll of enchant armour
This scroll adds one to the enchantment level of armour item chosen from the inventory (and uncurse the item, if it was cursed). This includes headgear, gloves, cloaks, boots, shields, or body armor. To identify the scroll you must enchant an item of armour when you read it.
Note that artefact items can't be enchanted, so this scroll can only be used to uncurse them, which is generally a waste, given that a scroll of remove curse will do the same task and is far more common. Body armor can be enchanted up to its base protection, so for example, a leather armour can be enchanted to +3, a plate mail to +10, etc. Bardings can be enchanted to +4, shields to +3, and all other pieces of armour can be enchanted to +2. Artefacts can be generated with higher enchantments. If a piece of armour can be enchanted further, this scroll will never fail, unlike scrolls of enchant weapon.
Enchanting armour to +5 will also make it immune to corrosion. This means, in practice, that the only mundane armours which can be made resistant to corrosion are heavier body armours, i.e. scale mails and up, as well as all dragon armours. Bardings can be made nearly corrosion-resistant, with a 98% chance to resist at +4.
Tips & Tricks
If you don't have an obvious use for these scrolls, you can save them for when you need to satisfy the requirements of the treasure trove portal. (And since they're relatively rare, if you don't have conservation, stash these as soon as you get them, lest they be destroyed by hostile fire arrows or magic.)