I'm trying to write with a ball-point ink pen on a plastic sandwich bag. When I try to write on some parts of the bag, no ink transfers to the bag: I can continue trying for quite a while in vain. I move to another part of the bag, and the ink transfers just fine. Then in other parts of the bag again, the ink will not transfer, and in yet others it will.
 I don't know what kind of plastic it is. The box only says "Ingredients: Plastic and Dye. SCJ Formula # 35*12700". (SCJ is S.C. Johnson & Son, Inc., the manufacturer.)