Round stars

Of all the possible ways to make stars, the method of making round stars is
probably the most interesting. A number of effects not attainable with other
methods become possible. Basically, round stars are made by sprinkling some
solvent over a core, followed by rolling it in a bowl containing some
composition. The composition sticks to the core, making it grow a little larger.
This operation, sprinkling and rolling, can be repeated as often as necessary to
obtain stars of the required size. The stars become spherical after one or two
layers have been added, hence the name. By adding subsequent layers of different
compositions, stars can be made to change color or effect in mid-air. On the
negative side, it does take a bit of practice to get good at rolling stars. I am
certainly no master of the art myself, far from it actually, but will do my best
to demonstrate the basics. If you intend to pursue this further, you may be
interested in reading the book 'Round Stars and Shells' by David Bleser. Check
out the literature
page for more details.

Cores
Several things can be used as cores. I heard of people using
among other things pieces of pasta, rice, all kinds of seeds, molecular
sieve pellets, lead shot and couscous. I personally find it easiest to use
cut or pumped stars. I have used rice with success as well. However, rice
does swell slightly when it is wetted which will cause the stars to crack.
This problem can be solved by first coating the rice with a thin layer of
waterproof lacquer. As an example, let's start with the flash #7 stars
described on the pumped stars
page and proceed to roll a layer of a charcoal streamer composition over
them. These stars will produce a yellow/golden fire dust streak across the
sky, followed by a bright twinkle of the flash composition when the stars
burn out. The ruler shows both centimeters (top) and inches (bottom)
btw.

Streamer composition
To produce the golden streamer effect, we
will use a simple potassium nitrate/charcoal/sulfur composition with a
very high percentage of charcoal. The charcoal particles will produce the
golden trail. To achieve the best effect, it is important to use the right
kind of charcoal. I've had particular good results using a mixture of 40
parts coarse (approximately 80 mesh) pine charcoal with 60 parts ball
milled willow charcoal. However, many types of charcoal will produce a
good tail and you can experiment with what's available to you. Mix 58
parts potassium nitrate with 35 parts charcoal and 7 parts sulfur, and add
an additional +5% of dextrin. Mix well (check out mixing techniques
if necessary).

Solvent
For dextrin bound compositions, a mixture of ethanol and
water is commonly used. I most often use a 25/75 mixture of ethanol/water
(parts by volume for liquids). The purpose of the ethanol is twofold.
Firstly, it reduces the surface tension of the water, allowing it to 'wet'
the cores and particles better. Secondly, it reduces the solubility of the
dextrin slightly which helps in preventing the cores from sticking
together initially. As the stars grow larger, the percentage of alcohol
could be reduced, increasing the solubility of the dextrin, which makes
the stars more tacky and allow them to grow in size more quickly. However,
I will roll the stars only to about 1 cm diameter this time and stick with
the 25/75 mixture untill done. Prepare the solvent and put it in a simple
spray bottle. You can usually adjust the nozzle of these to obtain a
directed but fine spray.

Getting started
Now we're all set to start rolling. Take the cores
and spray them once or twice with solvent. Immediately, shake them around
to distribute the solvent. Then, wait for a couple of seconds to allow the
solvent to soften the outermost layer of the cores and transfer them to a
bowl containing a little of the streamer composition. How much to use
depends on the amount of cores you started with, but it is not critical at
this stage. I used a few grams of composition. Roll the stars around in
the composition by swinging the bowl with a circular motion. This should
coat the cores with an initial layer of composition. However, this initial
step is usually the most troublesome. You will probably find that several
of the cores stick together and that they pick up very little composition
initially. Don't worry about it yet.

Sieving
Separate the cores from any composition they did not pick
up using a coarse sieve. If you used a composition with coarse particles,
like I used for the example, you will most probably see that the stars
have picked up the finer composition while the coarse particles remain.
The finer particles have a larger surface area and are less heavy, hence
they stick to the cores more easily. Later on, the stars will pick up the
coarse particles as well. For now, discard the coarse charcoal remaining.
Then, with the back of a spoon, separate the cores that stick together.

Growing further
Now, repeat the above a couple of times. Spray the
cores, roll them in composition and sieve. They should become quite round
after this. More importantly, they don't stick together as much and start
picking up composition more easily. Less of the coarse charcoal remains to
be discarded, and they grow much faster. Use just enough solvent to make
the stars appear slightly wet as shown in the before/after picture on the
right, but don't soak them. The picture also shows that most stars have
become nice and round, except for one or two that stuck together and were
not separated properly.

Larger still...
Now that the stars are large enough that they
don't stick together anymore and they pick composition more easily, it is
no longer necessary to separate them from any loose composition after each
addition. Also, since the total surface area of the stars has increased,
the amounts of solvent and composition have become much less critical.
Therefore, we can now simply keep the stars in the bowl with the loose
composition all the time. Spray them while maintaining the rolling motion
and add a little streamer composition. Keep rolling untill the stars have
picked it all up. Continue adding more small amounts of composition untill
the stars no longer pick it up, then spray with solvent again and begin
adding streamer comp again. Keep on going untill the stars reach the
desired size.

Size distribution
Because of slight differences in the dimensions
of the cores among other things, some stars will grow faster than others,
eventually yielding a batch of stars of variable size. Ofcourse, this is
undesirable if we like the stars to burn out or change color
simultaneously. Therefore, it is necessary to select the stars that are
done every so often during the rolling. For this purpose I use a plastic
box with holes of the desired size in the bottom. Dump the stars in, and
move them around. The smallest stars which are not yet done fall through,
while the larger ones remain. Return the small ones to the rolling bowl
and keep the ones that are done.

Drying
Spread the stars on a sheet of paper and allow them to dry
in the shade. Do not dry stars in the sun initially, as this may cause the
evaporating solvent to leave a layer of nitrate and dextrin behind. This
layer keeps solvent from inside the star from reaching the surface to
evaporate, and the star will never dry fully. Only after the stars have
been allowed to dry in the shade for a few days, they can be further dried
in the sun. If, like me, you live in a climate were sunny days are sparse,
you can use a dessicating agent such as anhydrous calcium chloride
(available in hardware shops) to fully dry the stars. If you do, make sure
the dessicant is not able to come into contact with the
stars!

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