Plates

[Sephrick]

The game automatically uses the required shards as long as you have a sufficient amount.

If you're getting those options, then you have the wrong hammer equipped. Both Armorer and Blacksmith use "hammers" and those are Blacksmith recipes

Here are the recipes:

Copper Plate, Bronze Plate, Brass Plate, Iron Plate, Mythril Plate, Darksteel Plate.