It is the weekend for our great national holiday. Time for folks around the country to (safely I hope) light off some pyrotechnics, perhaps sit back in a chair or recline on a blanket and view some professional displays of fireworks.
(William McIntosh - Flickr, Mark Twain Fireworks)
Time also to take advantage of an opportunity to convey to young inquisitive minds (and old and still curious folks) just how these brilliant displays come into being. A confluence of science and entertainment.
Fireworks - a brief history:
The earliest fireworks were entirely about making a loud noise, made by chunks of green bamboo chucked into a fire. Light was limited to that afforded by the fire in which these pau chuk chunks were chucked.
Basically, these simple firecrackers made noise when air trapped in pockets within the bamboo burst forth, splitting the chunks of pao chuk with a resounding report.
This was the state of the art for fireworks during the next thousand years.
Modern day pyrotechnics can trace their origins to two discoveries - both, also, from China.
The first of these discoveries was gunpowder, possibly as long ago as 900 AD. During the period between the Sui and Tang dynasties Chinese alchemists were seeking an elixir of life. Instead of such a magical potion they found a mixture of chemicals that would burn vigorously when being brought to dryness over a flame. One such formula was built around potassium nitrate (salpetre), sulfur, honey and arsenic disulfide (possibly a red hued orpiment). Now, the salpetre doesn't sound like it would invoke vigor, the arsenic is certainly toxic, perhaps then it is lucky that these alchemists concluded their mixture might be put to better use to enhance pao chuk.
Which they did.
The mysterious elixir was packed into the pao chuk. Throw the resulting packed bamboo chunks onto the fire and voila! Pao chuk on steroids - a very resounding large bang - the birth of the firecracker.
Over time improvements were made to this mysterious fire powder (huo yao) - eventually these yield something much closer to modern-day gunpowder. Higher salpetre content, the addition of a better fuel than honey (in the form of charcoal) and tweaking of the ratios of the formula lead to what friars accompanying the Crusaders probably encountered in the mid-13th century. This was then brought back to Europe - where it was initially turned to largely military aims. Eventually in Italy, during the Renaissance, they sought to perfect the more entertaining implementation of gunpowder in what we would recognize as a display firework.
Which was something the Chinese had been doing for centuries.
Both efforts ended up making aerial shells of improved power and variety of color and effect a centerpiece of their displays. Which was the second invention needed to make aerial shells.
All that was missing was color - the spectrum of effects being dominated by the orange flame and flash typical of burning gunwpder or carbon. Enough was known to see the benefits of adding powdered metal, sometimes yielding silver or gold sparks, but these efforts clearly lacked the range of colors one expects from a fireworks display this July 4th.
Let There Be Colored Light
We have Italian pyrotechnicians to thank for virtually ever color combination enjoyed in fireworks from about 1830 till the present day. Advances in science and chemistry led to the identification of pure elements, along with means thereby to identify when pure substances from these elements had been made.
They implemented formulas in which a specific pure compound of a suitable metal, combined with a source of chlorine (preferably chlorate in place of nitrate salts), were mixed with the other gunpowder ingredients providing pure colors of:
Red -- from a strontium compound, preferably Strontium Nitrate or Strontium Chloride;
White -- Typically produced from the already recognized metal powders such as zinc or , later, aluminum;
Blue -- Most typically from copper, always mixed with a heavy does of chlorine (less chlorine makes the color of ionized copper blue-green);
Green -- Barium compounds would yield a pure green;
Orange -- a nice pure orange comes from calcium, though a modified strontium-based formula (starved of sufficient chlorine) will also yield a red-toned orange;
Yellow -- Yellow comes from sodium. By far the easiest and cheapest to accomplish, also the hardest to avoid due to the ubiquity with which sodium is found throughout nature;
Pink -- A true pink can be made using potassium compounds(though it is very hard to find potassium compounds totally free of sodium, the yellow emission from which can readily swamp that of the potassium ions. A modified strontium formula can be substituted;
Violet -- Typically this is achieved through a balanced mixture of copper and strontium compounds.
Thus it was that the true spectra of hot ions emitted into the night sky became emblematic of the zenith of the pyrotechnicians skill.
So, this July 4th - let there be colored light!
And, please, be safe out there. Better a public display than a backyard burn-out.
Plus, be kind to pets. Few animals revel in firework displays.
Happy Independence Day.