When a white rose is properly prepared and placed in a glass of warm water containing food coloring, the petals begin to show the color within a few hours. It may take up to 24 hours, however, for the process to be complete.
Only freshly cut flowers should be selected for coloring. The stems should be cut on a slant to prevent the bottom of the glass from blocking the water intake. Warm water is absorbed more quickly than cold, so it produces faster results. A minimum of 20 drops of food coloring is required for every 4 ounces of water.