Bursting with pride

At a pier on Seonyudo, a small island on the Han River near Yeouido in Seoul, more than 20 workers are numbering thousands of pipes of different heights and diameters resting in wooden racks and spread over six barges.

"These pipes are called mortars and this is where the fireworks are launched from," says Jim Shih, general manager of Sunny, a pyrotechnics company from China. Mr. Shih is in Seoul for the Seoul International Fireworks Festival. His crew of 10 pyrotechnicians from Hunan, China, arrived in Seoul on Wednesday to prepare for their fireworks display Sunday on the Han River off Yeouido.

For the 30-minute show, more than 3,000 fiberglass and metal mortars were shipped two weeks ago from China, along with 3,000 shells and 100 "cakes" of multiple shells that will explode into thousands of points of light.

The brilliant flashes of light that explode to rousing music, the thundering booms and bangs, and the spectacular colors and shapes floating in the sky make fireworks a special summer evening treat. Anyone who has watched a fireworks show remembers being mesmerized by the lights as they bloomed into multicolored chrysanthemums, peonies and dahlias, or swayed like a willow and fluttered about in the form of butterflies before cascading down and dissipating into the dark night.

As magical as those lights may seem, what you see is the result of a series of chemical reactions.

The shells that are shot into the air look like cannonballs wrapped in brown paper. The mortars from which they're fired are usually about three times as long as the shells' diameter.

The shells can be as small as one inch in diameter and as large as 48 inches, and have pouches at the bottom containing black powder. When the powder, or lifting charge, is ignited and burns inside the snugly fitting mortar, the trapped heat and gas push at the sides of the mortar leading to an explosion that frees the heat and gas and hurtles the firework shell high in the air.

The makeup of that powder has remained the same since it was invented in China about 1,000 years ago: 75 percent potassium nitrate, 15 percent charcoal and 10 percent sulfur.

The shells contain dull black lumps, called "stars," which are about the size of a large marble. These lumps, when ignited, create the breathtaking flashes of color and light as they react chemically with oxygen.

A fireworks master is like a chemist, mixing carefully measured ingredients such as perchlorate and black powder with binding and coloring agents. Colors are achieved by mixing in certain metals: Magnesium or aluminum is responsible for brilliant white, sodium salts for yellow and strontium nitrate or carbonate for reds. Borium nitrate leads to green, charcoal ends up a glorious orange while copper salts lead to blue, a prized color because it is notoriously difficult to achieve a true blue.

As a shell ascends, a time-delay fuse embedded in it continues to burn. By the time the shell nears its apogee, the fuse will have burned low enough to ignite the bursting charge in the first compartment, or break, throwing out the stars.

But the show's not over yet. The fuse keeps burning, making its way to the powder in the second and third compartments. In a three-break firework, the middle break needs to ignite at the highest point in the shell's trajectory. If the timing is off, the firework might detonate too close to the ground. Hence, the designing of the fuse and calculating of their lengths requires great precision.

How wide the stars spread depends on the force released when the break bursts open. The more resistant the break, the bigger the display; resistance comes from the break's heavy wrapping which momentarily keeps the gas and heat from reaching the bursting charge.

No fireworks will ever be complete without the accompanying booms and crackling noises. These sounds actually come from sound charges that are sometimes contained inside a shell's break. The loud explosions, usually accompanied by a bright white flash, are created by using mixtures of perchlorate, a different kind of explosive than black powder.

The six barges with their cargo of mortar and shells will be pulled near Yeouido today where the wiring, probably the most crucial part of the operations, will be completed. On Sunday, two technicians will be at the master control board to control the timing of the fuses; one will be on a barge and the other on the spectator side. They will be checking the 20-page program sheet while listening to the sound track to make sure the explosions will be timed just right.

Mr. Shih's team has prepared a sound track of Chinese drums, Western classics, upbeat Ricky Martin songs and slower Korean music. "There is a one second lag between the music and the explosion when manual switching is used compared to a one-tenth of a second difference when computer synchronization is used," Mr. Shih says. Although more precise synchronization is possible with the use of a computer, even a small computer glitch can lead to everything going off all at once, or nothing going up at all -- both nightmare scenarios for any pyrotechnician.

Each culture has its favorite style. The Europeans, for example, like lots of noise with their pyrotechnics. Americans like brilliant colors and perfect synchronization with music. Japanese favor a lot of gold, the colors of changing maple leaves and symmetrical starbursts.

Sunday's show will feature a lot of red, a favorite Chinese color. "Look for fan-shaped displays, a unique feature of our program," Mr. Shih says. The shells Mr. Shih's team will be shooting have 12-inch diameters and weigh nine kilograms. Typically, they'll soar 250 meters high before exploding some 150 meters wide. "The last 30 seconds will be spectacular with fireworks exploding in all directions," Mr. Shih says.

China's Sunny Group will put on its fireworks show Sunday at Yeouido. The first shell will be fired at 8:30 p.m. The festival closes June 23 with shows by Italian and Korean fireworks companies. For information, call 02-783-3860.

by Kim Hoo-ran