I did some casting and had a rough finish like your and it was recommended to dust the mold with fine powder . I used talcum powder and had great results.
I hope this was helpful.
Hi I am building the 1/4 scale Merlin from a set of castings I purchased from a guy that did not have the equipment to make it.
I need some help withe the gears in the gear case as some of the plans are missing.
I am a new member and have been making engines for several years my last engine was a 1/3 scale LeRhone rotary. I am looking forward to seeing other builder work.