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I'm trying to write with a ball-point ink pen on a plastic[1] 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.

Why?


[1] 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.)

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May need better tags. –  msh210 Jul 18 '12 at 4:37
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It's probably surface contamination, like your fingers leaving oily residue where the pen can/can't write. Try with a new bag, and touch it. It can also be random stickiness issues with ball-points, the ball needs enough friction to roll. I think it's impossible to say without more careful experiments on your part, with different bags and different pens. –  Ron Maimon Jul 18 '12 at 5:00
    
@RonMaimon, thanks: surface contamination sounds plausible. Next time it happens I can try to wipe the surface with a dry paper towel or tissue and attempt again to write on the previously unmarkable spots. As to "random stickiness issues", note that there was consistency with respect to which areas could be written on and which could not. –  msh210 Jul 18 '12 at 5:07
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My advise would be to use markers instead of ball-point pens to write on plastic bags. –  Bernhard Jul 18 '12 at 7:16
    
Do the bags have a "write on" area? You do note that "there was consistency with respect to which areas could be written on and which could not." Does this consistency remain consistent across a variety of bags, or just the one bag you've already tried? Does the surface (table, paper, book) under the bag during writing change, or is different between the two areas? How about the angle of the pen, are you holding your wrist in the same spot while trying these different areas, thus changing the pen's angle relative to the bag? Are you writing the same thing, at the same size, in both areas? –  Adam Davis Apr 3 at 15:18
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