Thanks for all the replies, everyone!! Wow, I didn't realize just how many black iris there are out there. Unfortunately I have no details as to the vendor or when they were purchased. I was lucky enough to have them already in the garden when we bought the house. I have two other varieties of iris that also came with the house (neither of which I know the names of
though one is very similar to something called a 'maroon damask'), but these black ones bloomed a week or so later than those (they're still blooming now, I live in DC.) The blooms seem to be about 6", though I'm not entirely sure if I'm measuring them correctly. 'Before the Storm' seems like a good possibility, thanks for the lead lauriemorningglory! I will scour the database to see if I am able to pick out any other characteristics. Thanks again to all for welcoming this iris noob!