Combine the water and gelatin and heat gently to dissolve only, about 90°F/32°C. Remove from the heat and stir in the corn syrup and glycerin, if using.
Add the sugar and mix until smooth and well combined. Form into a log.
Lightly coat with shortening. Wrap with plastic wrap, sealing tightly.
Note: It is not necessary to refrigerate the fondant. Best results are achieved if the fondant is used the same day it is made, as it will tighten up overnight.