Ice Cube Soap Glycerin blocks Liquid food coloring Petroleum jelly Cotton swabs Ice cube trays (regular or with various shapes such as hearts) Cut glycerin into chunks, then place in a microwavable bowl. Melt the glycerin in the microwave on HIGH, stirring at 15-second intervals. About halfway through melting, add a drop or two of food coloring. With a cotton swab, coat the inside of the ice cube tray with petroleum jelly. Pour melted glycerin into the tray, filling each section almost to the top. Let cool at room temperature for about 2 hours. The "ice cubes" will pop out easily.