08-04-2011, 03:01 PM
As Sten explained, Enchantment Forges set and overwrite the property on the item - they do not increase an already existing property. Using your example you will need to remove the AC+1 via the forge, and then you will be able to add a better AC bonus if you wish.
Your other alternative is to look for enchantment gems by completing certain special quests *looks to Eltabbar* or getting those gems as a DM reward. Enchantment gems *are* stackable and don't take any XP or gold when used - so as a result are very rare. But if you would end up getting an Enchantment Gem AC +1 and use it on the armor in question, that will upgrade the AC from +1 to +2.
Your other alternative is to look for enchantment gems by completing certain special quests *looks to Eltabbar* or getting those gems as a DM reward. Enchantment gems *are* stackable and don't take any XP or gold when used - so as a result are very rare. But if you would end up getting an Enchantment Gem AC +1 and use it on the armor in question, that will upgrade the AC from +1 to +2.