AD&D Enchanting Magic Arms and Armor

As part and parcel of my research into making magic items, I still don't understand how one makes enchanted weapons and armor. If the weapon or armor has a special quality, like a flaming sword or armor of etherealness, then it's obviously a spell effect and there is a spell that matches or comes close in most instances. However, how does one make a +1 item? What differentiates a +1 item from a  +5 item?

I thought the spell enchanted weapon was the answer. It basically is a 4th level magic-user spell that makes a normal weapon function as if it were a magical one (presumably to be able to hit those pesky critters that require magical weapons to hit). But the spell does not itself give the weapon any bonuses to hit or damage, merely makes it equivalent to a +1 weapon to determine what it can hit (and still cause normal damage). Perhaps if this is used in conjunction with a permanency spell, then the item achieves true +1 status from the enchant an item spell? And perhaps multiple consecutive castings increase that value by +1 per spell infused. In order to make a +5 weapon, then, a magic-user would need five castings of the 4th level enchanted weapon spell, and be able to infuse them all at once.

So, if that's the workaround for weapons, how does one provide +1 protection for armor (and rings, cloaks, and other protective gear)? I suppose that could be a simple casting of protection from evil or similar spell that provides an armor class boost. Perhaps a shield spell? And how does that also confer saving throw adjustments? At least with protection from evil, the save bonus is inherent in the spell description.

Or maybe the plus is related specifically to the material from which it is made. There was a section in the DMG that broke down what all the armor types were made from, listing +1 to +5. Perhaps it's simply the act of making the armor magical that brings out the specific plus. In this way, a weapon, shield, or armor made from mithril will always have the same enhancement bonus, so long as it is enchanted in some way. Likewise, an adamantite weapon or armor would have a higher plus simply because of its construction. Therefore, a magical blade will never be made of simple steel as it could not possibly hold the enchantment (and probably why enchanted weapon does not provide a bonus to hit or damage).

Obviously this needs more research. However, it does seem to work and be supported by such instances as drow armor and weapons which seemingly absorb magical energies simply by being crafted in some way particular to the drow from these magical metals. It is important to note, however, that since they are not enchanted with enchant an item and permanency spells, their dweomer fades over time when removed from those radiations. Of course, that's just theory...