Here is where we need to take a discussion, even if in a new topic.Jeff H wrote: Over-application of any of these methods won't make it better, so you might as well let the mould cool and do some sprue-plate traige.
You just ... have to clean it off in addition to cleaning up metal surfaces with files and abrasive papers.
I'm sure there's more than one ham-fisted casting newbie out there that has scored a mold...