I have just been painting my shoulder bells and after reading post about liquid mask and not having a clue about it I use some glue I had to hand. Copydex, as it is called here in blighty. It is like a laytex rubber type of glue (can be quite messy). Painted it on, painted my colour and simply peeled off when dry, worked a treat and did not harm the previous coat. I have a massive bottle so problem solved.