After assembling the Pillow Vase vessel form, it's often too dry to decorate right away. If that's the case, I can either re-hydrate it by draping with a damp rag and placing in a plastic bag or brush the surface with slip intermittently before adding the decoration. Once the piece is moist enough to successfully accept the decoration - moist but not so plastic that the clay will buckle at all with any pressure), I can apply whatever decoration I choose - spirals made from extruded clay, rosettes cut out from a thin slab of clay or slip decoration using a pastry bag and various tips.
For this "frosted" decoration, I use a pastry bag with a star tip. I score and then slip around the vase's opening and along its waist - the location of the join between the two parts of the vase. In the case of those tiny vases with a "pansy frog" (see two vases to the right side of the picture to the right), I mark a circle that encompasses all the openings and score and slip around it. (By slipping the scored area, the applied decoration does tend to conform to the piece more successfully.) I apply a circle of rosettes around the opening first, then around the waist, thus minimizing the risk of "messing up" the work I've already done. I'll either use my finger or a tool of some kind (doesn't really matter which), I clean the opening of any encroaching clay before setting it to dry. It's important with these pieces to make sure to sand the decorated area before bisque firing as the slip can dry into very sharp edges.