I know that when you fail to enchant a weapon past +3, you lose the weapon and get some crystals in compensation. I don't remember exactly how much it gives, I think it's something about half of the weapon's value in crystals. But now, I heard that you get more crystals when you fail to overenchant if the weapon was overenchanted already. The higher the weapon is enchanted, the more value in crystals you get when you fail.
Now, does anyone know exactly how it's calculated? What value in crystals you get when you fail at +5, at +7, at +15 ?
If nobody knows, maybe we can figure it out by pooling everyone's data. I'm quite sure that the same equation could be applied to every weapons/armor/accessory. Please write down:
The weapon's name and grade
The weapon's enchantment when it failed (failed enchanting from +5 to +6)
The weapon's SA (if it had one)
The quantity and grade of the crystals given
afaik, u get half of the crystal value of the enchant scrolls additional to the half the crystals for the weapon.
The crystal value of a scroll can be calculated by deviding the NPC shop sell price and the NPC shop sell price of crystals (e.g. Enchant armor D grade has a crystal value of 11, if my math is correct ;) )
+16 Dark Screamer blowing at going for +17 gives 2165 C-crystals ;) Take away the base crystal count and then divide the amount with 16 and it might be the number for C-grade. Not sure if the numbers grow in a linear way tho.
I didn't believe you receive crystals for the SA, just the scroll and the weapon. I realize it costs gemstones and adena to activate the SA, but that's part of the risk of enchanting a weapon with an SA:)