If it happens so that you've got enough ingredients in your inventory to make an item, but they're not shown in the Item Workshop, you need to make sure that these items do not have artful qualities.
As you know, there are items that possess artful (unique) properties. They're sold in the Royal Shop and there's a certain chance that you'll make one in the Item Workshop. These items cannot be used for making other items, i.e. you need a non-unique one to use it for crafting.
The only exception are the items from the Dominator's set. They require artful ingredients.