Any free standing candle, embed or tart use a mold to be created. Molds come in many shapes, sizes and materials. The three most common types of material a mold is created from is aluminum, plastic and silicone. Aluminum molds are generally used for free standing pillar candles, they can be used over and over because of their durability. Plastic molds are generally used for votives, embeds and tarts. Plastic molds are available in many shapes and sizes, they can also generally be reused. A plastic mold used for tarts are often sold with the tart. Plastic molds can warp when the wax is too hot so keeping an eye on pouring temperature is important. Silicone molds are perfect for tart or wax embeds. The silicon material allows for the heat to escape more easily then aluminum therefore cooling more quickly. Silicon molds have the easiest release and clean up.
When using any mold especially aluminum make sure to first spray with Mold Release Spray, this will help to ensure the wax comes out more easily. If you are still having trouble getting the wax out you can put the mold in the fridge for an hour or so. If your wax is brittle the cold temperature of the fridge could cause the wax to break.