17th June 2009, 09:07 PM
Sounds like it might be post medieval blast furnace slag. Medieval and Roman slag tends to be a dark colour and very dense and heavy especially tap slag. Smithing slag can be more vesicular but is still denser than blast furnace slag. I also think I remember seeing some small degraded looking pieces which were pale grey and vesicular and dated to the Iron Age, so it's a bit difficult to pass an opinion without seeing your material.
By the way, hi everyone. First post!
By the way, hi everyone. First post!