There's a glitch with the crafting/construct when trying to make level 80s armor from the diamonds. When you drag the 2 karat or 3 karat diamond to the crafting menu, in both case the 1 karat diamond is listed as the ingredient instead. So only the 1 karat diamond is available for crafting which ever karat diamond you insert.
Crafting bug
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There's a glitch with the crafting/construct when trying to make level 80s armor from the diamonds. When you drag the 2 karat or 3 karat diamond to the crafting menu, in both case the 1 karat diamond is listed as the ingredient instead. So only the 1 karat diamond is available for crafting which ever karat diamond you insert.