Ask A Scientist Chemistry Archive

Question:  This question was asked of me on July 4 and I didn't know the 
answer.  How do pyrotechnicians add color to fireworks and how do they 
vary the shape to create such diversity within the show?
kenbel

Answer:  I'm so glad someone asked this...pyrotechnics is my hobby!  The 
colors are generated by adding different inorganic salts to the 
exploding mixture.  Barium salts produce greens, strontium makes red, 
sodium makes yellow/orange, potassium makes purple.  The whites and 
golds are made with mixtures of iron, magnesium, aluminum.  One you 
probably didn't see was blue (you can say you did, but I bet you 
didn't!) Blues are produced by using copper salts.  But copper is very 
touchy.  In every explosion, the heat generated excites electrons to 
higher energy levels.  When they relax, they release the color.  Copper 
tends to decompose at too high a temperature.  Result:  no blue.  If it's 
not hot enough, the electrons won't be excited enough to emit color.  Again, 
no color.  Pyrotechnics companies are still doing research with this one.  
Every once in a while you may see a blue one...they got lucky.  As for the 
shapes...again, research.  The shells being hurled into the air are a little 
bigger than a bowling ball (the real big bursts are about 500 ft in diameter.  
They are packed in a way that the effect-creating particles come out in the 
desired shape.  Believe me...none of this is chance!

Greens are produced by barium salts and reds are made with strontium salts.
When the shell explodes, it excites the electrons of the atom to a
higher energy level.  When the electrons relax, they emit characteristic
light for a particular element.  I'm glad someone asked this...
pyrotechnics just happens to be a hobby of mine and a colleague is a
consultant for the Bartalotta Fireworks Co.  here in Milwaukee.
Did you hear the whistlers?  Those are made by using a chemical mixture
that produces a standing wave in a cylinder when it's burned (and no,
I can't give a recipe!  It's potassium perchlorate and sodium salicylate
is all I really know).  As the level of the mixture gets smaller, the
wave gets longer, frequency lower, and thus a lower pitched sound (if my
physics is correct).  It's not a Doppler effect with a mechanical
whistle of any kind.  Probably more than enough info here.
-Joe Schultz (jschultz)