Give me an 'A.' July 4th displays get an explosive new look: fireworks you can read.

You're lying on a scratchy blanket, craning your neck at this year's July 4th fireworks show. Oooh! A red explosion! Aaah! Gold sparks! Hey, wait a minute . . . . the word "WOW"?

After years of experimenting, fireworks engineers can now splash letters and numbers across the sky. Words are the grand finale of the latest and greatest type of fireworks, called shape shells. Instead of exploding into a common old starburst, their points of light spread out into a perfectly recognizable outline.

Hearts, stars, and peace signs have graced the skies at July 4th celebrations for several years. Letter shells, however, debuted only last August at the Republican National Convention. What did they spell? D.O.L.E., of course, with an elephant shape to boot. Now, letter and number shells will hit July 4th celebrations all over the U.S.

MASTER BLASTERS 

What goes on when shape shells-- and traditional fireworks--go off? To find out, there's no better source than the Brookhaven, N.Y., factories of the Grucci family. Dubbed the First Family of Fireworks, the Gruccis invented and perfected shape shells. Masters of pyrotechnics, the science of fireworks, the Gruccis have been splashing colors across the sky for more than 150 years.

Pyrotechnics is basic chemistry dressed in flashy clothing. All fireworks work essentially the same way. Each display begins as a papier mache shell filled with a mixture of powdered chemicals. When the shell is lit, the chemicals react with each other; the bonds between the chemical atoms break and rearrange themselves to form new substances.

In fireworks reactions, that rearranging process releases loads of energy--more than it took to get the reaction started. That's called an exothermic reaction. The energy is released in three forms: heat, light, and sound. The last two are the key ingredients of a Grucci display.

GETTING READY

The first step in creating a display is to make a fireworks shell. Grucci workers fill the cavity of an empty shell with marble-sized black balls called stars (See diagram on pp. 14-15). Stars are chemical-packed pellets that emit brilliant colors as they burn and burst outward from the blast.

"It's easy to arrange the stars in a round circle that bursts uniformly in the sky," says Phil Grucci, who brainstormed the letter shell idea. "It's much harder to make points and angles and asymmetrical (uneven) shapes like letters."

So, for the shape shells, the trick is packing the stars so they make a recognizable shape when they burst.

Then, the stars are surrounded with black powder, similar to gunpowder. When the black powder explodes, it blows the shell apart and sends the stars sailing.

Grucci workers also add long fuses to the shells. The fuses ignite the black powder once the shells are in the sky. Finally, the Gruccis tack on lift charges to the base of the shell. These are small explosives that boost the shells high into the air.

SHELL-EBRATION

On the day of the show, each shell is loaded into a long metal tube called a mortar. The mortars are set up on the launching field, aimed skyward.

At showtime, a worker uses an electric match to generate a spark that lights both the lift charge and the fuse. Chemical reactions, after all, don't happen automatically. It takes a jolt of energy to get things started-- to break the original chemical bonds. The spark provides this activation energy.

Then, as the crowd holds its collective breath, the shell shoots out of the mortar. The flame runs along the fuse, racing toward the shell. When it makes contact, the real thrills begin.

FROM FUSE TO VIEWS

Two chemical reactions produce the burst of color in the sky.

First, the fuse ignites the black powder inside the shell. BANG! Chemical bonds shatter and reform, releasing energy. This exothermic reaction blows the shell apart: It transforms the mixture of chemical powders into hot gases that expand suddenly.

There's not much to look at yet-- just a flash. Then, in an instant, the heat from the black powder ignition provides the jolt needed to ignite and propel the stars. Technicolor time!

The stars stream outward, propelled by the expanding gases. As the chemicals inside the stars react with one another, they create streaks of colored light. Ooh! Aah! Another exothermic reaction!

And don't forget the energy released from both reactions in the form of sound. It may take a few more seconds to reach you because light travels so much faster than sound.

All-in-all, it's a lot of work for the letters W-O-W. But, the Gruccis hope your eyes (and ears) will be dazzled.

For more about fireworks, check out this Web site:

http://cc.oulu.fi/-kempmp/pyro.html