I need some help with a problem we are having with our green sand patterns. We are a green sand ductile iron foundry, so it is no the cleanest environment. Our 420 and 304 patterns are plagued with a film of green sand building up on them when we first put the patterns in the molding machines. After pulling the patterns out and wiping them down a few times, the sand no onger sticks. All of our SS patterns have lost their luster and are very dull in appearance, even with all of the friction between the molding surface and the sand. I have sampled cleaning tha patterns with an abrasive and with Nitric acid to remove the excessive oxide layer. Initially the patterns shined and no longer had any sand sticking but in a few days they were highly oxidized again. I am looking for some suggestions for a long term fix.