Recently, I’ve made a batch of welded compression molds out of black iron sheets  since they’re easier and cheaper to resource. Once the molds were welded, I’ve coated the exterior with high temp. spray paint (used for car parts). But after baking it and leaving the coat to settle, parts of the paint still tends to come off when heated. So, I’ve left the inner molds un-coated for now.

Even after sanding and cleaning off the rust, there are still traces of rust and dirt that stick to the plastic once it’s released from the mold. Which makes clean up a bit more tedious.

Are there any recommendations to prevent rust? I’m considering making mold out of stainless but I find it pricey.