Shell hemispheres

Different sizes of shell hemispheres

Shell hemispheres are hollow hemispheres filled and jointed to create spherical shells. Stars are lined up against the wall of the hemispheres, filled with a break charge and closed. Commercial hemispheres are either made of plastic or strawboard. The former are made by injection molding, the latter by forming strawboard cutouts by pressing into hemispherical moulds. The japanese frequently also use a third type called newspaper hemispheres to manufacture high-quality shells for the internal market only. Note that similar containers can be cheaply made at home using kraft or newspaper and paste. In the case of plastic hemispheres a solvent such as Xylene or Methylene chloride is used to seal around the equator of the shell.

In constrast to those made of plastic, paper hemispheres, once provisionally jointed with a piece of tape, are further elaborated in a time-consuming process called pasting. Pasting involves saturating strips of paper with paste and glueing them on to the hemispheres in multiple layers.

Shell Construction

If you don't have time to make your own paper aerial shells, then commercial paper shells can be used. Making your own shells casings is quick, easy and more importantly cost effective. First step is to wrap one layer of cling film plastic tightly around the foam ball. The plastic wrap prevents the first layer of glue covered craft paper from sticking to the foam ball. Once you have wrapped the ball, twist it tightly and cut off the excess with a sharp pair of scissors. Take a small amount of paper tape and secure the twisted end to the ball to prevent it from unravelling.

Cut your craft paper into thin strips and using a small paint brush, lay a strip of craft paper onto a newspaper and lightly apply the glue to it. Wrap the strip around the equator of the sphere and place another strip 90 degrees from the first. At this stage you can roll the sphere on a solid surface to effectively iron out the paper wrinkles. Add another strip to the exposed part of the sphere and then another at a 90 degree angle. You should now no longer see any of the exposed area of the cling wrap. Do this process 3 more times until you have achieve 4 layers of craft paper.

Using your thumbnail, locate the equator under the craft paper and using a razor blade gently cut along the equator line until the shell forms two hemispheres. Do not remove the craft paper from the foam ball, set them aside and let dry overnight. Once the halves have dried remove the inner foam ball.