Cut several marigolds with a pair of garden shears or sharp scissors. Choose marigolds that have just begun to bloom, and cut them during the warm part of the day, when the air is dry.
Purchase some silica sand at a garden supply store. Put about 1 inch of silica sand in the bottom of a large tray. If you don't have a tray, any large, flat container such as a cardboard box will work.
Remove the stems from the marigolds, and lay the blooms on top of the silica sand, with the blooms facing up. Add more silica sand to the top of the marigolds, until the flowers are completely covered. Set the tray in a cool, dry place and check the blooms every other day. When the marigolds are dry, the petals will feel like paper.
Poke a length of floral wire carefully through the head of the flower. Wrap a piece of green floral tape around the wire.