This file was originally intended for teachers of chemistry as a short 
introduction to pyrochemical demonstrations. However, the compositions and
the methods of preparation are indeed general, and the stars prepared here
can be used for most pyrotechnical applications, including starmines and
bombshells.
Enjoy.





Pyrochemical reactions in chemical education - Part I:
Coloured smokes, coloured flames and sparklers
A. Introduction

As an assistant leader of our chemistry club, I've often been asked to 
perform some chemistry magic tricks before the audience. I know from
personal experience that probably the most interesting demonstrations
are those demonstrating the true magic of chemistry - that is, chemical
reactions. Those who have a fume cupboard (hood) for demonstration 
purposes can broaden their spectrum of useful demonstrations by including
the most beautiful effects known to mankind to their demonstration sets - 
namely, pyrochemical reactions.

Many demonstration manuals (notably Shakhashiri's Chemical Demonstrations)
include several reasonably safe "flash'n'boom" demonstrations. However,
while these demonstrations are relatively easy to perform and do not
require any special equipment, they still fail quite often and unexpectedly.
This is often due to high sensitivity of the compositions, which prevents
the demonstrators from making accurate preparations.

The thermite demonstration looks great, but it is usually performed in a very large scale. If you haven't tried it before, or if you change anything, try
it first (preferably outside) without any audience before performing it live.
Also, make sure it will go off when you want it. I suggest using a good fuse
and black powder instead of the methods presented in the manuals. Magnesium ribbon burns with a dazzling flame, but it is neither a fuse nor a match.

The demonstrations presented here are based on tiny pellets of the 
composition held together with a binder. They are also called stars.

These are not as rapidly prepared as the usual demonstration compositions,
but contrary to these, the stars can be safely stored in metal cans. They
are at least as safe as matchheads. A 50-gram lot of stars is good for 
tens of demonstrations.

Binders are organic compounds designed to keep the star in one piece. They
may be ordinary resins or gums (like shellac), carbohydrates (dextrin),
plastics (polyvinyl chloride, Parlon rubber) or thermosetting resins 
(polyurethane, epoxy resin).

Chlorine donors are compounds designed to add chlorine or hydrochloric acid
to the flame. In coloured flames, they serve three main functions:

1) They aid in evaporation of the emitters (colour-producing substances).

2) Usually, the emitters are themselves chlorides (or diatomic species
containing chlorine) of the colour-giving elements. Metal chlorides cannot
be added directly, since they usually attract moisture.

3) In magnesium-containing compositions, the chlorine donors reduce the
disturbing background radiation of magnesium oxide and makes the flame
transparent. The chlorine donors also cool the flame.

The most common chlorine donors are polyvinyl chloride (PVC) and Parlon
rubber. The latter is richer in chlorine (ca 70%). They can both be used as
binders, too. Ammonium perchlorate is the only practicable oxidiser which
simultaneously acts as a chlorine donor.

Preparation of dextrin:

Spread some flour or potato starch on a plate and heat at 220 oC in an oven
for 15...30 minutes. Avoid overheating - when the product is brownish and
readily soluble in water, it's ready. Dextrin can be used either as a mere
fuel or also as a binder. Water is used as a solvent in this case. Sometimes
dextrin is mixed dry with the other ingredients and water is added 
afterwards. However, see instructions below for a safer alternative.

Shellac and red gum may also be mixed with the other ingredients (if they
are powdered) and ethanol used as a solvent. Red gum is also called accroides resin. Shellac and red gum are also good fuels. 

Parlon rubber is soluble in acetone.

Notes on using PVC:
PVC is available in two forms, hard (unplasticised) PVC and plasticised, 
flexible PVC. Unplasticised PVC is available from PVC manufacturers.
Plasticised PVC is the form used for practical purposes. It contains some
high-boiling organic liquids (plasticisers) to keep it flexible.
It is very useful in pyrotechnics, too. Plasticised PVC tubing or hose 
can be cut into pieces and dissolved in tetrahydrofuran (THF).
This solution can be used as such. It can contain up to 18% of PVC (w/v), 
but give a week or two for the PVC to dissolve. A solution of hard PVC is 
rather messy to handle. It is advisable to add 2 parts of dibutyl phtalate, 
dioctyl phtalate or tricresyl phosphate to the solution per 100 parts of PVC
as a plasticiser. Instead of cutting the wet star composition into pellets
with a knife (as described below), you can just let a PVC-bound mass alone
on a plate until it's dry, carefully remove it and cut it into stars with
a pair of scissors. Easy. But only with plasticised PVC.

Unfortunately, THF is the only practically useful solvent for PVC. It is
really expensive, and if you want to reduce costs, use some other
binder and powdered PVC. 

Tetrahydrofuran, ethanol and acetone are all narcotic if inhaled. Work in 
a fume cupboard (hood). Stains of the binders are sometimes hard to
remove. Plasticised PVC is the easiest, but shellac requires hot ethanol
and probably some detergent for successful removal.

The stars are normally prepared as follows (this is probably the safest

method):

1. Dissolve the binder in the solvent used (usually water or ethanol). Pour
the solution into a flat plastic bowl and mix in the other ingredients.
Make sure all the ingredients are thoroughly moistened before adding the
next one. This will almost entirely exclude any accidental friction between
the fuels and the oxidisers. You can use glass or stainless steel tools for
mixing. Grind all the ingredients _separately_ in a mortar before weighing 
and mixing them.

2. After you've arrived in a more or less homogenous mix, allow the excess of the solvent to evaporate (care! do not allow the mix to become too dry, since you'll have to moisten it again!) and press the mass into a flat cake, about 8 mm thick. With a pizza cutter, cut the cake into cubes 8 mm each side. A knife or a ruler may also be used. Best results are achieved by keeping the cutter clean. Allow the mass to dry (in a safe place; you may use a fridge fan to aid in drying) and remove the stars by bending and twisting the bowl. This is why we used plastic. However, see note on using PVC above.

3. Sometimes it is necessary to coat the stars with an igniting composition.
This can be done by moistening the stars with a suitable solvent in a bowl
and sprinkling the igniting composition on the stars. Give the stars a good
shake before adding more solvent or powder. It is advisable to mix
a little binder into the igniting composition before using it for coating.
For example, if you're going to coat the stars with black powder, you should
add some (say, 5%) dextrin to the black powder and moisten the stars with
water. Do not use _too much_ solvent - the stars will stick into each other,
and you'll get only large lumps! Use a dropper for adding the solvent.

You can mix your own powder for coating. It isn't actually true black powder,
not even "meal powder" (mixed and ball-milled powder), but it serves this
purpose well.

75 parts of fine, sieved potassium nitrate
10 parts of fine sulfur (preferably flour)
15 parts of fine, sieved charcoal

This mix can be stored in small plastic containers. 
Specific procedures are described below if they are needed. The above 
procedure is usually appropriate.

B. Coloured smokes
These formulas contain volatile organic pigments, which will partially
evaporate (sublime) from the heat of the main composition (lactose/potassium chlorate). Dextrin is used as a binder. The stars are usually coated with black powder to ensure ignition. It is advisable to use these stars in a cardboard tube to prevent the smoke from catching fire, which will destroy the effect. The easier alternative is to use a wire gauze (as usual) and to blow the flame out. 

Note that the low flame temperatures of these stars aid in formation of 
possibly toxic by-products (comparable to campfire smoke). The dyes 
themselves are quite safe, although Rhodamine B should be handled with care
- it stains everything and contact should be avoided.

1. Blue smoke

40 parts of copper phtalocyanine (Phtalo Blue)
25 parts of lactose (milk sugar)
33 parts of potassium chlorate
2 parts of dextrin (a water-soluble binder)

Add water and proceed as above. Coat the stars with black powder/dextrin
or a simple ignition composition consisting of 

4 parts of potassium chlorate
1 part of sucrose (cane sugar)
1 part of dextrin

This time you'll have to mix the chemicals in a dry state, ie, as plain 
powders. Use a small plastic bowl and a glass rod for mixing. Do not grind.
Do not store the composition. Sprinkle it on the moistened stars. Use at 
least 20% of the weight of the stars.

2. Yellow smoke

43 parts of quinoline yellow (quinophtalone yellow, Chinolingelb)
24 parts of potassium chlorate
16 parts of lactose
6 parts of sodium hydrogen carbonate (sodium bicarbonate)
2 parts of dextrin (as a binder)

Add water, proceed as above. Like the blue smoke stars, these stars should
be coated either with black powder or the igniting composition described
above.

3. Red smoke

40 parts of Rhodamine B (C.I. Basic Violet 10, C.I. 45170)
24 parts of potassium chlorate
16 parts of lactose
4 parts of sodium hydrogen carbonate
2 parts of dextrin

Add water and proceed as usual. Coat the stars as above.

Many other organic pigments and dyes can be used in coloured smokes.
The dyes should volatilise (sublime) readily between about 300...450
degrees oC, which excludes almost all dyes containing -NO2 (nitro) or -SO3H
(sulfonic acid) groups. Unfortunately, the leftovers are usually the
malicious azo or anthraquinone dyes, with known toxic properties. The dyes
suggested here are all safer than them.

If you wish to develop your own formula for a dye you think should work,
just substitute the dye with Rhodamine B in the previous formula. Every
dye would require a formula of its own, but the third formula is a good
starting point. If the dye you're using is evaporates near or slightly
above 300 oC, use a) 45 parts of the dye instead of 40 parts and b) 8
parts of sodium hydrogen carbonate instead of 4 parts.

C. Coloured flames

These are both easier to prepare and use than the coloured smokes. The
colours result mainly from atomic and molecular emissions in the flame.
For the yellow colour, the emitter is atomic Na (two lines near 589 nm).
For the red, both SrO and SrCl (radical) act as emitters, the former 
giving a series of bands around 610 nm, and the latter emitting near 660 
nm. Green comes from the molecular emission of BaCl radical (a number of
bands in the 510...535 nm range), but the colour is often disturbed by
BaO, which emits a series of bands mainly in the 530...600 nm range 
(yellow). Moreover, BaCl is unstable at above 2000 oC. Finally, blue can
be obtained from the emission of CuCl below 1200 oC. The temperature of
a typical Bunsen flame is about 1800 oC, and the primary emitter at that
temperature is CuOH, which gives a green flame. The secret of a vivid blue
is a cool flame.

If you use the stars for demonstration purposes, it is not necessary to coat
the stars, since they will readily take fire anyway. The chlorate
compositions are generally more sensitive than the perchlorate compositions.Avoid sparks and static electricity. Do not grind!

1. Red stars

20 parts of potassium chlorate
60 parts of strontium nitrate
20 parts of shellac (binder)

Dissolve shellac in boiling ethanol. Add the other ingredients and proceed
as described in the introduction. The stars take unexpectedly long to dry.
They can be dried in the sun or in a vacuum, but do not try any heating! The 
smaller the stars are, the faster they'll dry.

65 parts of potassium chlorate
15 parts of strontium carbonate
20 parts of shellac

Proceed as above.

44 parts of potassium perchlorate
31 parts of strontium nitrate
8  parts of polyvinyl chloride (PVC) _or_ 7 parts of saran (PVDC)
15 parts of red gum (accroides resin)
5  parts of shellac (binder)

Proceed as above. 

30 parts of ammonium perchlorate
35 parts of potassium perchlorate
18 parts of strontium carbonate
2  parts of hexamine
2  parts of fine charcoal
16 parts of red gum (accroides resin)
4  parts of dextrin

Add water, proceed as above; _but_ do not coat these stars with black powder! Ammonium perchlorate and potassium nitrate (from black powder) react to produce ammonium nitrate and potassium perchlorate. Ammonium nitrate is hygroscopic; the stars will never be dry in ambient humidity.

The following coating composition can be used:

80 parts of potassium perchlorate
15 parts of fine charcoal
4  parts of red gum (accroides resin)
9  parts of manganese dioxide (optional!)
4  parts of fine aluminium (preferably fine flake or pyro grade; optional!)
2  parts of dextrin

Aluminium and manganese dioxide aid in ignition, but are not necessary.

2. Green stars
A simple but nice (somewhat yellowish) green can be made from

7 parts of barium nitrate
7 parts of potassium chlorate
2 parts of shellac

Dissolve shellac in boiling ethanol and proceed as described above for red
stars.

Dazzling green:

50 parts of barium nitrate
32 parts of lab grade magnesium powder
18 parts of Parlon (chlorinated isoprene rubber) 
or 18 parts of PVC (corresponding amount of the solution in tetrahydrofuran)

Mix Parlon with magnesium. Add 50 volume parts of acetone, mix well and
mix in the other ingredients.

If PVC is used, add the correct amount of the solution in THF to the other  ingredients and proceed as described above for PVC.

The composition leaves lots of ash. Ammonium perchlorate improves it:

56 parts of barium nitrate
32 parts of lab grade magnesium powder
17 parts of Parlon rubber (or PVC, solvent: THF)
25 parts of ammonium perchlorate

Proceed as described for the previous composition. Use 60 volume parts of
acetone for Parlon. If you use PVC, use the procedure above for using it.

Greens can also be based on aluminium:

65 parts of barium nitrate
10 parts of very fine aluminium (preferably dark pyro grade (sic!))
20 parts of Parlon rubber
4  parts of sulfur
2  parts of boric acid

Add acetone and proceed as usual. Coat with black powder.
An improved, fierce-burning formula with ammonium perchlorate:

65 parts of barium nitrate
20 parts of saran (or parlon, but saran is better in this case)
3  parts of red gum (accroides resin)
7  parts of sulfur
10 parts of very fine aluminium, preferably dark pyro
15 parts of ammonium perchlorate
2  parts of boric acid
2  parts of dextrin

Beautiful green, without magnesium:

50 parts of ammonium perchlorate
35 parts of barium nitrate
15 parts of shellac

Dissolve shellac in boiling ethanol and proceed as usual.

Twinkling green (wow!)

23 parts of magnesium powder (use any lab grade powder)
60 parts of ammonium perchlorate
17 parts of barium sulfate

Binder solution: Dissolve 3 parts of nitrocellulose (smokeless powder or
celluloid film) into 30 parts (w/v) of boiling acetone. If you're going to
prepare these stars more than once, prepare more of the solution,
since nitrocellulose dissolves slowly even in refluxing acetone. Approx. 
30 parts of the solution (v/w) is used each time.

Mix the ingredients into the binder solution in the order they appear above.
Proceed as usual. Note that acetone evaporates very rapidly and the stars
usually dry within a few hours.

Magnesium reacts slowly with ammonium perchlorate producing ammonia and magnesium perchlorate, especially in the presence of moisture. Thus, the
twinklers cannot be stored for more than 6 months, and they must be kept
in a closed bag.

During the smoulder phase, magnesium reacts with ammonium perchlorate
in the dark. In the flash phase, magnesium reacts with barium sulfate,
producing hot MgO and creating a green flame. The flash is followed by 
another cycle, since the flash rapidly consumes the reactants in the flash
zone. 

Nitrocellulose is used as a binder, since other binders tend to interfere
with the twinkling.

3. Blue stars

60 parts of ammonium perchlorate
17 parts of sulfur
20 parts of copper(II) oxide CuO
6  parts of red gum (accroides resin) _or_ shellac (powdered)
3  parts of dextrin (binder)

Add 25 volume parts of water to dextrin and mix in the other ingredients.
Use more water if necessary. Proceed as described above for stars in
general.

63 parts of potassium perchlorate
13 parts of copper oxide
14 parts of Parlon rubber (binder) or PVC (solution in THF)
10 parts of red gum or shellac (powdered)

Mix red gum or shellac powder with Parlon. Add 50 volume parts of acetone,
mix well and mix in the other ingredients. Proceed as usual.

65 parts of potassium perchlorate
16 parts of cuprous chloride (CuCl)
10 parts of sulfur
11 parts of Parlon rubber (or 12 parts of PVC)
7  parts of red gum (accroides resin)

Use either Parlon or PVC as a binder. 

60 parts of ammonium perchlorate
20 parts of copper(II) oxide CuO
10 parts of sulfur
10 parts of dextrin
12 parts of polyvinyl chloride PVC (use a solution in THF)

Add the PVC solution to the other ingredients. Allow some THF to evaporate, 
form a cake 1 cm thick and allow it to dry on a plastic plate (check that it
doesn't dissolve in THF!). Remove the dry cake and cut it into stars with a
pair of scissors.

4. Yellow stars

6 parts of potassium chlorate
2 parts of sodium hydrogen carbonate
2 parts of dextrin

Mix dextrin with 4 volume parts of water and mix in the other ingredients.
Proceed as described above for stars in general.

D. Sparklers, silver rains

Sparks are produced whenever hot liquid or solid particles are expelled 
from the flame. In pyrotechnics, charcoal and aluminium are the most
common sources of sparks. Magnesium does not produce good sparks,
since it evaporates at 1100 oC and usually burns completely in the flame.
Charcoal and iron sparks are often orange or golden yellow, whereas Al
sparks are whiter. The colour of a glowing solid or liquid particle is almost
completely determined by its surface temperature. The intensity distribution often obeys the Planck's black-body radiation curve, although the actual intensities are usually lower than the theory predicts. This has sometimes been called grey-body radiation. The intensity maximum shifts towards shorter wavelengths (blue endof the visible spectrum) as the temperature increases. At the same time, the overall intensity is markedly increased.

The sparkler composition must generate enough gases in order to expel
the hot particles. Moreover, if the burning proceeds mainly through liquid
phases, it reduces the amount of sparks remarkably. Thus, ammonium 
perchlorate is ideal for sparklers and silver rains. Potassium perchlorate
and potassium chlorate are generally not used, except with potassium
nitrate. The particle size of the materials may also have a profound effect
on the quality and quantity of sparks, especially with aluminium. Fine 
flakes are best. 

Dextrin and shellac are usually used as binders. Epoxy resin and polyurethane
can also be used. 

The spark compositions are safer to prepare than coloured stars, since they
don't usually contain chlorates. Still, we are using fine metal powders here,
and the unpelletised compositions may be powerful explosives, though not 
especially sensitive. Powdered aluminium is most sensitive to static 
electricity. When in doubt, use metal cups and wear cotton clothing. Or,
even better, add all the ingredients to a solution of a binder one at a time.
This will exclude any danger in the preparation. The dried stars are not
as dangerous as the plain powders.

Furthermore, the stars may be hazardous to use, due to their very nature.
Have a fire extinguisher handy and wear cotton clothing. I also advise you
to protect your face and eyes. As always, remember not to test the stars
the first time before the audience. The shelf life of the stars is quite
long.

The stars are prepared as usual. Since fine powders are used, the stars are
easy to cut.

1. Gold flitter

16 parts of fine potassium nitrate
3 parts of sulfur
2 parts of powdered charcoal 
4 parts of sodium oxalate (or 2 parts of ultramarine)
11 parts of fine, grey aluminium powder (preferably pyro aluminium)
5 parts of flake aluminium or medium aluminium powder (Al bronze works well)
4 parts of dextrin (binder)

Add water and proceed as usual. The particle sizes of aluminium powders
will markedly affect the result. If Al bronze is available, you can use all
16 parts of it instead of the two different Al powders.

2. Silver shower I

35 parts of potassium nitrate
8 parts of fine charcoal
2 parts of boric acid 
7 parts of sulfur (flowers of sulfur)
60 parts of potassium perchlorate
20 parts of fine pyro aluminium (atomised aluminium, 0.1 um)
25 parts of fine flake aluminium (Al bronze)
15 parts of coarse flake aluminium 
10 parts of dextrin

Add water and proceed as above. As before, the particle size and surface
area of the reactants has a profound effect on the results.

3. Silver shower II

65 parts of ammonium perchlorate
22 parts of fine aluminium powder or flake aluminium (not too coarse)
18 parts of shellac

Dissolve shellac in boiling ethanol, mix in the other ingredients and 
proceed as usual. Shellac stars take a long time to dry; try drying in the
sun. The particle size of aluminium is not as critical as in the above
formulas.

4. Simple silver shower

15 parts of flitter (or any grade except the finest pyro grades) aluminium
55 parts of potassium nitrate
2 parts of boric acid 
10 parts of fine charcoal
5 parts of dextrin (binder)

Add water and proceed as usual.

If you don't want to obtain N+1 grades of unspecified Al powders, feel free
to experiment with the grades you have. Both stabilised and unstabilised
Al powders will work. Just substitute the powder you have with the Al
powder suggested in the formula. (Use small batches.) If the composition
burns too fast and emits only a few sparks, you have to add coarser
grades. If you have enormous difficulties with ignition as well as a poor
result with regard to sparks, your Al is too coarse. 

E. Uses
The stars should be used in a fume cupboard (hood), since they emit large
quantities of irritating smoke. There are several alternatives for ignition.
My own method is to place the stars on a wire gauze and ignite them with
a Bunsen burner. Use only a few stars at a time. The twinkling green stars
should be used one at a time for the best effect.

The stars will burn for a few seconds. They usually leave very little 
residue. Clean up with a wet cloth and wash the gauze with water.
The effects can be used for demonstrating a variety of principles: 
thermochemistry (the heats of reactions), kinetics and activation energies
(why don't the stars go off at once?), electronic spectroscopy (atomic
and molecular emissions), the chemistry of chlorine compounds (chlorates
vs. perchlorates), phase changes (evaporation of dyes) and even complex
kinetics (oscillations), if you can use the magnificent twinkling stars.

F. Hazards
The preparation and use of pyrotechnic compositions is not free from danger.
The smoke compositions are relatively safe, since they contain many inert
materials. Coloured flames, on the other hand, are more hazardous to 
prepare. Follow the instructions carefully and avoid all grinding or static
electricity. Do not prepare too large batches (20...50 grams is ideal for
a beginner). Dry and store the stars in a safe place and label them. Do not
store any powdered compositions.

The stars won't explode, but the loose powders may have a good chance of
doing that, especially when confined. The stars merely burn (and are a fire
hazard if they are accidentally ignited) and generate noxious smoke.

By following the instructions, the preparation and use of ready-made stars
is at least as safe as the pyrotechnic demonstrations described in 
Shakhashiri's great demonstration manual (Chemical Demonstrations: A hand-book for Teachers of Chemistry, part 1.)

Disposal: The best way of disposing old stars is to burn them. They can be
safely burned in small batches (no more than 50 grams at a time) if you use
a safety fuse and some igniting composition. Do this _outside_. If this is
not possible, do it in smaller batches in a fume cupboard. It is advisable
to have a fire extinguisher handy, as always.

G. Pyrotechnic literature
John A. Conkling: Chemistry of Pyrotechnics (Marcel Dekker, New York, NY
1986)

A great textbook for anyone, especially for those who are interested in the
chemistry beyond the fireworks.

See also Conkling's great articles in Scientific American (July 1990, pp
96-102) and Chemical & Engineering News (June 29, 1981, pp 24-32). 

T.Shimizu: Fireworks - The Art, Science and Technique, 2nd ed. (Pyrotechnica
Publications, 1988)

This book is a must for any professional, either for a pyrotechnist or a
teacher. A comprehensive treatise of commercial fireworks and the underlying science.

More references can be found in Books in Print (in most libraries).

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