Scotch Bonnet Seashell

Piping a seashell can be tricky; they have so many tiny details that make them unique (and last I checked there isn't a piping tip marked "seashell"; you just make do with the same tips you use for everything else). The official state shell of North Carolina is the Scotch Bonnet (pronounced "bonay") and the only tips you'll need to pipe an approximation of it are round tips #12 and #5. You'll also need stiff consistency royal icing, a flower nail, parchment paper squares, a glue stick, a Styrofoam block to rest the nail in, and a dusting pouch filled with a 50/50 mix of powdered sugar and cornstarch. Start by sticking a parchment square to the flower nail with a dab from the glue stick. 

 Hold the #12 tip just above and at a 45 degree angle to the surface. Squeeze out a ball to anchor it, then increase pressure while pulsing the tip in and out to create ridges. As the icing builds up, decrease pressure while continuing to form ridges, then stop pressure and pull the tip away.

 You might need to dust your fingertips to adjust the tip or pinch off any excess.

 Switch to the #5 tip and pipe a lip around the lower left half of the shell. When the icing is dry, peel away the parchment. You can use a brown food-safe marker like the Gourmet Writer by AmeriColor or a small brush and some brown Color Dust to dab in a pattern of dots (in this photo you can see why the shell's name was inspired by Scottish tartan).