Seashells are primarily calcium carbonate, such as eggshells. Theoretically, Easter egg dye should function on seashells since it does on eggs, however shells in the ocean aren’t as stale as shells from cattle. The exception is worn old shells, abraded enough to absorb dye easily. So, the challenge when dyeing seashells would be to bring an acid into the dye which will break down the shells and encourage them to absorb the color. It’s not a precise science, and you’ll get varied results using leftover egg dye, food coloring and vinegar or textile hanger.
Prepare the egg dye according to the package instructions, adding vinegar to help the dye penetrate the shell. Add 1 tablespoon of white vinegar and 1 tablespoon of coloring into a cup of water if you are using food coloring. Use 1 tablespoon of dye per cup of water to get fabric dye.
Wash and dry the shells prior to immersing them in the bottles of Easter egg dye, food coloring or fabric hanger. A dry shell absorbs more fluid. Cover the shells completely in the dye bath.
Keep checking to see whether the dye is taking and how quickly the color deepens. Weathered shells using a bit of a chalky surface absorb more dye than newer, smoother shells. Most dyes deliver results in about 30 minutes.
Remove the shells from the dye containers and permit them to dry on a baker’s rack or sheets of craft paper. Eliminate the wax bathtub.
Clear-coat the dyed and dried shells using lacquer to protect the color.