Scroll of enchant armour
Reading a scroll of enchant armour allows you to immediately add one to the enchantment level of any piece of armour item in your inventory (and uncurse the item, if it was cursed). This includes headgear, gloves, cloaks, boots, shields, or body armor. Unlike weapons, armour will always improve when affected by these scrolls unless they are already maximally enchanted. Whether the attempt succeeds or not, using the scroll on a piece of armour will identify it.
Note that artefact items can't be enchanted, so this scroll can only be used to uncurse them. This is generally a waste, as 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 (for example, leather armour can be enchanted to +3, plate mail to +10, etc.). Barding can be enchanted to +4, shields to +3, and all other pieces of armour to +2. Artefacts and (rarely) acquirement gear can be generated with higher enchantments.
Enchanting armour to +5 will 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. ring 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. 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.