Mix the latex mold kit following the manufacturer's directions. Pull off a golf ball-sized piece of latex mold, flatten and then firmly press the leaf at least 2 inches down into the mold.
Allow the mold to dry, per manufacturer's directions, and carefully pull the leaf from the latex.
Put on protective gloves and a smock and a respirator mask. Even when working with a small amount of concrete, it is essential to protect yourself from burning or breathing the highly alkaline concrete dust.
Pour about 6 cups of concrete mix into the bucket. Add the dry pigments, if desired, and water, and mix with wooden spoon until the concrete is the texture of cake frosting.
Spray the inside of your latex leaf mold with vegetable oil, coating it evenly.
Scoop prepared concrete, using the wooden spoon, from the bucket and pack it into the leaf mold. Tap and shake the mold slightly to ensure that the concrete fills all areas of the mold and dislodges air bubbles.
Scrape away excess concrete around the edges of the mold and allow it to dry for four to six hours.
Peel the latex leaf mold away from the concrete and set it aside.
Repeat the process for each leaf desired.