I quote myself because Peter read my question to Brandon and expanded the answer a bit (three tweets put together) Peter:  Oh, I think Aluminum would stop Shardblades from magical cutting. But if it's too thin like foil, a sword... would cut it anyway. What I'm arguing is that something else that Shardblades don't cut doesn't need... to necessarily be made of aluminum, for various reasons. Me: For example Invested objects (metalmind,spike,ecc) or polestones (from some SA's Quote)