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If you don’t have cornstarch available, use powdered sugar instead. Then, use your hands to smooth and shape the fondant without leaving fingerprints. After you’ve smoothed the fondant, you can dust off the cornstarch with a clean paper towel or even a soft, dry paint brush. Pour a small amount of powdered sugar over the fondant, and spread a light coating over your work surface. Use a brush or your hands to coat the ball of fondant and the counter. Fondant is made of sugar, so adding a bit more won’t change the flavor or texture.  If you find that the fondant sticks to the surface as you’re working, you can add more powdered sugar. Alternatively, you can use a light dusting of corn starch for the same effect. However, you won’t be able to apply more cornstarch after the initial application, since it can give the fondant a gritty texture. If fondant is left in the air for too long, it will harden and go bad. Only knead as much fondant as you can use within 30-45 minutes, and wrap the remainder in plastic to keep it moist and clean. Once the fondant hardens, you won’t be able to use it. Some people keep their fondant in airtight containers and store them in the refrigerator while they work. If you do this, you may have to knead for a longer period of time. Coat 1-2 fingers in a small amount of shortening, and then run them along the tear. Use your fingers to slightly pinch the fondant together and smooth it out. This will help repair the hole and keep it from tearing further. Never use water to fix a tear, as it can cause the sugar in the fondant to dissolve, making the tear worse.

Summary:
Coat your hands in cornstarch before handling fondant so you don't leave fingerprints. Dust your fondant with powdered sugar to keep it from sticking to surfaces. Keep excess fondant wrapped in plastic to prevent drying and crumbling. Repair small tears in the fondant by rubbing shortening on the area.