For piping decorations, melted chocolate is often transferred to a cone created from parchment or wax paper. It cannot be piped from a pastry bag with a metal tip, because the melted chocolate tends to harden as soon as it comes into contact with the cool metal.
To start, melt the chocolate, but let it cool for a few minutes so it is slightly less viscous. If the chocolate is too warm, it will be too liquid and not hold its design when piped.
To make a paper cone, cut a large triangle from the corner of a piece of parchment or wax paper. The base should be at least 12 inches long. Consider the top of the triangle as point A, with the left corner B, and the right corner C. Hold the triangle at B and C, with A pointing up. Bring B diagonally up to the right, and C diagonally up to the left, and the paper will start to form a cone, with the tip directly across from A (1). Continue tightening the cone, keeping the tip as sharp as possible, until B and C meet at A. Fold all three points down into the cone to secure it (2). Stand the cone up in a tall glass (3). Pour the melted chocolate into the cone (the tip should be tight enough that the chocolate doesn’t leak). Close the cone, and fold over the right and left corners to enclose the chocolate (4). Snip the tip of the cone with scissors to make a small opening, about 1\16-inch wide, just large enough to allow the chocolate to flow freely.