Behind the scenes: Festival fireworks

THE EIF BANK OF SCOTLAND FIREWORKS CONCERT

EDINBURGH CASTLE

FOR most of the year, the small bunker-like room adjacent to Mills Mount Battery houses the One O'Clock Gun Exhibition, illustrating the history of the daily lunchtime bang for visitors to Edinburgh Castle. Since last Sunday, however - as during the last week of every Edinburgh Festival - it's been the operational nerve-centre for another resounding Auld Reekie tradition, the annual Bank of Scotland Fireworks Concert.

Trestle tables serve as makeshift desks, littered with laptops, walkie-talkies, coffee cups and the odd banana, while stapled to the walls are dozens of A4 sheets, each covered with rows of hand-drawn hieroglyphic symbols. These represent a minutely itemised map of Europe's biggest pyrotechnic spectacular, detailing the type and location of hundreds of individual firework formations, currently being unloaded, checked and set in position by the 15-strong team from Pyrovision, the company who design the display each year.

Outside, as Bat Out of Hell blares from a truck radio, technicians are busy inspecting several dozen racks of heavy-duty metal cylinders, ten to a rack, each tube holding a single three-inch shell. Come Sunday night, these will explode in successive starbursts of colour high over Princes Street Gardens where, far below us, looking like ants, workers are setting out the seating in the Ross Bandstand.

"Every rack is individually labelled according to colours, location and electrical sequence number before we get here," says Keith Webb, who runs Pyrovision with fellow firework artist Wilf Scott. "Then they all get counted again and re-checked against the plans: if someone's miscalculated, we don't want to be finding out on the night."

Sunday's 45 minutes of son et lumière represents the culmination of a month's hard graft back at Pyrovision's depot - and that after Webb and Scott spend two weeks designing the show, with initial planning having begun last autumn.

"Pretty much as soon as we've recovered from one fireworks concert, we start thinking about the next one," says Rod Bain, concerts administrator for the Scottish Chamber Orchestra, who liaises with the Festival, the pyrotechnicians and the sponsors to produce the show. "We start by programming the repertoire, which involves certain basic restrictions: for technical reasons it's difficult to set off fireworks for longer than 12 minutes without stopping, and obviously you don't want too many slow, quiet sequences - although little bits of that work really well. In general, though, we like to come up with something a bit different or unusual for Pyrovision to get their teeth into."

Webb and Scott between them draw on several decades of experience in creating world-class firework displays, for events ranging from the Queen's Golden Jubilee to Pink Floyd's "The Wall" concert in Berlin. "The more fireworks I've seen and designed, the more I tend to visualise in colour when I listen to music," Webb says. "I'll hear certain sounds and see patterns, or I'll pick up on themes and picture them as motifs throughout the show. Fireworks technology is always moving on too, so new effects become available, and with this show in particular, there's always the challenge of outdoing yourself from previous years, which I like - I'm not a believer in 'that'll do'."

As of yesterday, most of the works were already in place along the castle ramparts, including the 100-metre cable linking 70 high-voltage units, that will send the famous silver-white waterfall cascading down the Castle Rock. The primary task now is to finish laying the two miles of electrical cable, and wiring up the thousands of connections that will detonate around three tonnes of high explosive. Since Wednesday, meanwhile, Webb has been sitting in on the SCO's rehearsals, or listening repeatedly to a recording of the concert programme, in order to fine-tune the intricate, split-second timings for the show.

"Working with a live orchestra is much trickier than using recorded music," Webb says. "Our timings are already complicated by factoring in delays, like the four seconds a shell takes to get up in the air before it explodes - and then the conductor might take things faster or slower on the night than in rehearsal, so we have to compensate as we go along. During the concert, I'm in constant contact with the orchestra's score-reader, who anticipates and gives me the cues. As well as a live sound feed, I've also got CCTV coverage of all the firing positions, so I'm in touch with everything that's going on, minute to minute - and this is a long show for us, by far the longest we do: 45 minutes is a lifetime in fireworks terms."

Remarkably, once months of preparation have gone up in smoke, the load-out for the show takes a mere two hours - after which, surely, there's some serious celebratory unwinding to be done? "Not really, I'm afraid," Webb says. "It's been a very long week by that point, and everyone's shattered, so it's usually just a case of back to the hotel, a beer and a sandwich - and then off to bed."

• On Sunday the SCO, conducted by Clark Rundell, will perform Bernstein's Overture to Candide, Gershwin's Overture to Strike up the Band, Barber's Adagio for Strings, Ives' Three Places in New England and Copland's Rodeo: Buckaroo Holiday. For further information, tel: [phone] or visit www.eif.co.uk