Decorate a cake for an engagement celebration with a gold- or platinum-toned fondant ring. For a bridal shower, make a batch of cupcakes and top each one with a miniature version of the fondant engagement ring. You can colour the ring to make it gold or platinum to coordinate with the bride's ring and add an edible diamond gemstone for a realistic-looking embellishment. For a bride who prefers gemstones other than diamonds, use different-colour edible gemstones to make sapphires, rubies, emeralds or even topaz.
Place a small package of fondant in a mixing bowl and add a bit of yellow food colouring when making a yellow gold ring. If you are making a platinum-coloured ring, leave the fondant white.
Roll the fondant between your hands to make a log that measures approximately 4 inches long by ½-inch in diameter. You can adjust the size of the ring to accommodate the size of the cake. When topping cupcakes with the fondant rings, make the logs 2 inches long by ¼-inch wide.
Wrap a sheet of waxed paper around the paper towel roll and tape it in place. Wrap the fondant cylinder around the roll. Pinch the ends together, then smooth the ends with your fingers for a continuous circle. If the fondant log is too long, cut off the excess at one end and then pinch the ends together.
Stand the paper towel roll upright to keep any indents in the working surface from shaping the fondant. Add an embossed design to the ring with a toothpick if you would like. Let the ring dry for at least six to eight hours.
Mix some silver or gold lustre dust with lemon juice. Add just enough lemon juice to make the mixture watery. Paint the mixture onto the ring and let it dry for one to two hours.
Remove the ring from the roll. Pull the roll out gently, then remove the waxed paper from the ring.
Melt a few clear, edible gemstones in a saucepan and pour them into the diamond silicone mould. Let the candy cool for two to three hours in the refrigerator.
Cut a toothpick in half. Insert one end into the edible diamond and the other end into the ring to make a diamond.
Place the ring on top of the cake or insert a toothpick into the side opposite the diamond and stand the ring upright on the cake.