How does a Bless Spell work when last on items

In AD&D ( and later versions), a Bless spell can be cast upon an item to make it blessed. Example would be a blessed finely cured piece of leather for an Armor spell or a blessed crossbow to slay a Rakshasa. Im not clear about how Bless spell applies to items used in this nature. Does the blessing last only as long as the spell, requiring a cleric to cast a bless spell prior to those items being used.Or can you just cast a bless spell on a piece of leather or crossbow bolt and its considered blessed from then on? Furthermore, how many items can you bless with a spell at one time, since bless is usually an area affect spell that boosts allies. Can it be cast on a pile of leather scraps and crossbow bolts or only one at a time. I don’t see where its clear in how to use bless when required for other reasons other than blessing the party.