Hi, I saw a post you'd made in 2009 about the white sharpie pens at merry artists. I have two questions. First, you said it was extra fine and that one I see is the oil paint pen, but the fine is for the poster paint and that was what the link took us to. Which do you use, the oil paint extra fine, or the poster paint fine? Second question, do they last if you don't use them for awhile. That's my issue with the Signo ones. If you leave it sit for a couple months, it won't work anymore. Thanks so much.