Summarize:

If you’re dyeing an old candle, the easiest option is to simply reuse the original jar. However, almost any type of container will work, provided it’s heat-safe, has an open mouth, and is large enough to hold the melted wax. Metal cans, shot glasses, tea cups, and mason jars can all make great DIY candle molds.  Use gelatin molds or empty tea light holders to pour multiple miniature candles. To make free-standing candles with the wax exposed, try cutting the top off of a quart-sized milk carton. You can then tear the cardboard away once the wax has set. Take an uncut wick and tie one end around a wooden dowel or pencil. The opposite end should be just long enough to reach the bottom of the container. Set the dowel over the open mouth so that the wick is perfectly centered and hanging straight down.  A wooden clothespin or strip of tape can also make a decent wick holder in a pinch.  To create a double wick for a larger candle, simply tie a second wick 1.5–2 inches (3.8–5.1 cm) away from the first. It may take up to an hour for the wax to solidify completely. As it does, it will assume the shape of the surrounding container and you’ll have a brand new homemade candle in your favorite color. In the meantime, avoid touching the wax. Doing so could leave behind depressions, smudges, or other imperfections.  Be careful not to disturb the wick while the wax is setting up, as well. Placing the freshly-poured candle in the refrigerator or leaving it in another cool area may help speed up the hardening process. Untie or cut the wick from the dowel. Take a pair of scissors and snip the wick about 1⁄4 inch (0.64 cm) from the surface of the wax. Your new candle will then be ready to light and add a warm glow to any room! Clipping the wick too short may make the candle difficult to light, while leaving it too long will cause it to burn inefficiently.
Select a container for the new candle. Position the wick in the empty mold. Allow the wax to set up. Trim the wick.