Wow, very cool. Love the history and the mystery of them. I am betting they are hallmarked but are so tarnished/corroded that the hallmark is covered over.
If these were mine (and I sure wish they were!) I would take them to an antiques dealer or appraiser, maybe a pawn shop, that would be willing to identify the material they are made of for you, without cleaning them. Once you know what they are made of, then research if they should be cleaned or not. The corrosion could add to their value/character, or it could be destroying them. I think you're going to need a hands-on identification of the material.
What ever they are made of, they are a fabulous find! How exciting it must have been to pull these out of the ground!