Remove all leaves around the rose stem and cut the tips of the stems at a diagonal angle.
Fill a clean vase with a few inches of very warm water.
Mix in several drops of black floral dye. There are different dyes available on the market, but try to purchase a floral dye at a florist or craft store. If you can't find floral dye, you can try black food coloring.
Mix in one packet of flower preservative with the water and dye mixture.
Add another 2 inches of a floral hydration pretreatment solution to the vase. You can find hydration pretreatment solutions at most florists and floral stores.
Add the roses to the vase. As the stems absorb the water and dye solution, the petals will begin to turn black.
Change the water in the vase after a few days. Use clean water mixed with a floral preservative, which will help preserve your black roses for several more days.