When piping the Zinnia, the ball flower center has a lot to do with the final shape. For a perfectly shaped flower, make the ball a little flatter, more like the shape of a half orange.
Buttercream icing medium consistency
Step 1: Use Flower Nail No. 7. Hold decorating bag fitted with tip 7 at 90° angle to nail surface. Pipe a ball and slightly flatten with finger dusted in cornstarch.
Hold decorating bag fitted with tip 101 at 45° angle with the wide end of tip touching the outer edge of the ball. Pipe a row of zigzags for petals. Repeat for 3-4 more rows, each time angling the tip up a little more.
Add five tip 1 dots to center.