Heat oven to 212 degrees. Mix confectioners' sugar, cornstarch, gum tragacanth, and CMC together, and warm the mixture in oven for 10 minutes.
In a microwave-safe container, soften the gelatin in 2 tablespoons cold water.
Add glucose and vegetable shortening to gelatin-water mixture. Warm in microwave on medium-high power until the gelatin is dissolved and the glucose and shortening have melted, 1 to 1 1/2 minutes.
Transfer warm confectioners'-sugar mixture to the bowl of an electric mixer fitted with the paddle attachment. With the mixer on medium speed, add the gelatin mixture, then the egg white.
Change to the hook attachment, and beat on high speed until a ball forms, about 10 minutes. When you pat the sugar paste, you should be able to hear a hollow sound, which indicates that the gum paste is ready. If paste is too stiff, add additional egg white or water. If paste is too soft, add additional gum tragacanth or confectioners' sugar.
Remove the gum paste from the mixing bowl, and lightly rub shortening on the surface to prevent drying. Wrap in plastic, and store in an airtight container for 24 hours before using.