I knitted this reversible tank from a book by Sally Melville called The Knit Stitch. It is knit in garter stitch only. The vertical ridge was made by just slipping a stitch from the right needle to the left needle instead of knitting it. I used worsted weight yarn 70% cotton / 30% rayon. It was a lot of fun to make and only had to be joined together with seams at the shoulders. Front and back are buttoned up. One side has a V neckline and the other side has a U neckline.