I do not say this to rain on your parade, but being a full-time rare book, art and antiques dealer I have consigned to Sotheby's five different items in the last twelve years, and they usually want the item to have an estimated value of at least $10,000. I think you should try to find a more suitable auction house that's deals exclusively or almost exclusively with sunken treasure and artifacts. I think there are a few good ones in Florida. Also, did you send the pictures to the specific department's email that deals with this kind of artifact, or just to Sotheby's general email? The reason I ask, is that it might take a few weeks (at least) to receive a reply (since they get tons of appraisal requests each day) from the general email. If you want to pursue Sotheby's, I would get a hold of the correct department, call and speak to someone in that department, telling them what you have, and then send the pictures to your contact. You'll get an answer much quicker that way.