Chrysanthemum Shell (4")

A spherical break of coloured stars, similar to a peony, but with stars that leave a visible trail of sparks. A common composition to give the trails are slow burning gunpowder mixtures. The addition of large amounts of charcoal causes thousands of glowing charcoal sparks. The sparks are made alive at first by the action of nitrates on the charcoal then the air supplies oxygen later on in the sparks life.

A black powder propelling charge (lift charge) is used to project the aerial shell into the air and are fired from high-density polyethylene (HDPE), fibreglass or heavy walled cardboard tubes. Upon firing, the lift charge is consumed and the shell is projected from the mortar. The pyrotechnic effect is produced near the highest point of flight when a burst charge within the shell explodes, dispersing the stars. As the star burns it leave behind a trail of charcoal sparks and then finally all the stars change colour.

[edit] Shell casing

Casing
For a casing you will need a 4" paper ball shell. These can be purchased from most on-line pyrotechnic supply stores however it is much more economical to make your own and it gives you total control in regards the the shell wall thickness. This tutorial will demonstrate the construction process of the shell hemispheres.

Star composition
4" chrysanthemum shells normally require about 1cm diameter coloured stars (or larger if you wish). The coloured star is then coated in a charcoal based composition to give the long trails as the star is thrown through the sky. The addition of large amounts of charcoal causes thousands of glowing charcoal sparks. The sparks are made alive at first by the action of nitrates on the charcoal then the air supplies oxygen later on in the sparks life. Potassium nitrate based star compositions which are high in charcoal aid the long tail effect. In this example we will be using Chrysanthemum 6 as it has a wonderful, relatively long lasting tail effect and are easy to make and a red perchlorate star core. Do not use chlorate based stars if the charcoal composition contains sulfur.

Burst charge
Strong burst charge such as whistle mix is recommended, H3 can be used unless your stars contain sulphur. Flash powder can disturb colour perception if the flash is too bright. Of course, if you use stars that are based on a chlorate composition (which is strongly discouraged for beginners) black powder burst should never be used as it contains sulphur. Sulphur makes chlorate compositions very, very unstable and spontaneous ignition will most likely occur. In this example we will be using whistle mix.

Meal coated rice hulls are used to help break the shell apart without shattering the stars to dust at effect time. In the core of this we will be adding a small amount of whistle mix.

Time fuse
Visco fuse works well for small shells. For larger shells, proper time fuse is better. If you are unable to source time fuse or visco fuse then black match may be used.

Glue
You will need good quality white glue.

Other
You will also need paper tape, scissors, tissue paper.

[edit] 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 unraveling.

Cut your craft paper into thin strips and using a small paint brush, lay the strip of craft paper onto a newspaper and lightly apply the glue to the strip. 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 spear 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.

[edit] Star Construction

There are several formula's that can be used for the tail effect and colour core for chrysanthemum stars. What ever composition you choose to use, as the star is projected across the sky the charcoal composition must leave a good trail of sparks referred to as streamer arms or tendrils. It is not recommended aluminium flitter be added to the composition as this will increase the burn rate.

More coming on star construction...

[edit] Burst Charge

A chrysanthemum shell needs to project the stars out a great distances at high speed and a 4" shell needs a strong burst charge. In this example meal coated rice hulls are used to help break the shell apart without shattering the stars to dust at effect time. In the core of this we will be adding a very small amount of whistle mix burst charge.

Take an old toilet roll tube or similar and cut it neatly in half. Place both halves of the shell hemispheres on top of the tubes so they don't roll around. Using a felt tipped pen mark a location for the fuse and drill a 1/4 inch hole in the fuse location and hot glue a length of time fuse cross matched on the end external to the shell.

Make a thin tube by rolling a length of kraft paper a couple of time around a 1/4 inch piece of wooden dowel (or you can use a plastic drinking straw). Slide this over the time fuse on the inside of the shell and secure it in place with some hot glue. Cut the tube off so it's just under the rim of the shell.

Fill the tube with granulated black powder leaving enough space for you to insert a small piece of rolled up tissue paper. The tissue paper does not have to be a tight fit, it's purpose is to prevent the black powder from falling out when the shell is turned over. You can now add the chrysanthemum stars into the shell hemisphere. Arrange the stars around the wall of the shell one layer deep only. Do not load the stars above the rim of the shell, as this will prevent the two halves being snapped together later.

Next take a handful of meal coated rice hulls and place them into the center of a piece of tissue paper. Now carefully place the tissue paper into the shell half without the time fuse. User your fingers to evenly spread the meal coated rice hulls around the shell. The purpose of the tissue paper is to prevents the stars from working themselves away from the shell wall into the center of the shell during transport or launch. Trim the tissue paper all around the shell and make sure that it doesn't extend above the rim.

Take another tissue paper and tear a small hole in the center. Slide the hole in the tissue paper over the paper tube or straw and push it gently all the way to the bottom. Get a cupful of meal coated rice hulls and empty the entire cupful into the shell and spread the hulls around evenly with your fingers. Again, trim the tissue paper all around the shell and make sure that it doesn't extend above the rim.

Now you need to dump a spoonful of whistle mix into the center of each hemisphere. Flash powder can be used but it can break the shell too hard smashing the stars into dust, or it may shoot them out so fast that they blow out.

To assemble the shell place a square piece of cardboard on top of one hemisphere and turn it over whilst firmly holding the cardboard in place which prevents the contents falling out. Carefully align the two hemispheres together and slowly retract the cardboard. Once the two halves are aligned use a few strips of paper tape to join and seal the shell. The tape needs to be applied to the equator.

To finish the shell you will need to apply approximately 13 layers of 70 lb craft paper using white glue and apply them evenly around the shell. You can either use a large round wooden dowel or a hard surface to press and rub out any wrinkles in the paper. It is best only to apply 4 or so layers at a time otherwise the shell surface will become soft, unmanageable and shrink when drying.

An easy way of loading the aerial shell into the mortar tube is to first measure the depth of the mortar with a ruler and add 10cm to this. Cut a piece of string to this length and attach one end of the string to the crown of the aerial shell (opposite to the fuse end) with some paper tape or similar. Make sure the weight of the aerial shell can be held securely with the string. This will ensure when the aerial shell is lowered into the mortar tube the time fuse will be sitting in the lifting charge and pointing in the correct direction. When you have lowered the aerial shell into the mortar leave the excess amount of string hanging over the edge of the tube, this way if you need to remove the aerial shell for any reason it can be done easily. Remember, never ever pass any part of your body directly over the mouth of a charged mortar. A mirror should be used to inspect the interior of the mortar.

Attach a paper cone lifting cup with about 25 grams of granulated 2FA black powder (you may need to adjust this quantity depending on the final weight of your shell and inner diameter of mortar) over the time fuse. Cut a small hold with a sharp knife into the cone and insert your quick match and secure in place with glued paper tape. Your chrysanthemum aerial shell can now be loaded into the mortar.