So, I have been running into a problem with all of my aluminum molds. I am getting lead deposits on the mold face while casting. Some times they will wipe off with a dry rag when the mold is up to casting temperature but most of the time they will not. The deposits get built up enough that it allows me to see light between the mold blocks when they are closed. I am casting at around 720 degrees with a soft lead with tin combination. I do not add sprues back to the pot as I am casting. I am really trying to figure out a way to first figure out what is causing this issue and then a way to clean the offending material off of my mold faces. It's really disheartening to have a brand new NOE mold be disfigured by this issue. I've attached pictures of the issue in question. Any held would be much appreciated. Thank you.