How can I safely make sparks for a film shoot?

March 11, 2006 4:08 PM

I'm looking for a safe way to generate a lot of sparks for a film.

In the shot the character is connecting a large power source to an electronic device, like a computer. When he does it I really want the thing to light up with sparks. The only ways that I can think to do this don't seem very safe. I can shoot the sparks separately and composite them in afterwards.

I've considered doing the whole thing as a computer-generated special effect, but I'm sure that it will look fake.

posted by MattS to Technology (17 answers total)

1) welding kit (blue sparks)
2) sparklers (white sparks)
3) chain attached to car, driving down the road (not sure how you'd composite that in)

If you don't want to rent a welding kit yourself, why not see whether the local construction crew would let you film their work?
posted by aberrant at 4:15 PM on March 11, 2006

sparklers (as in 2 above) taped to the back of something metal should throw sparks into view without doing anything more than scorching whatever they're taped to.

I'd test this somewhere safe, but I'd bet you could insulate a wood surface with tin foil (shiny side out) and use the sparkers on it without doing any real damage.

This could work as long as you don't mind the sparks coming from around the corner or over the edge or something.
posted by tiamat at 4:22 PM on March 11, 2006

If you want realistic sparks of the kind you get at the point of connection when you connect a huge power source to something totally unprepared for it, you definitely want footage of an arc welder in operation - because that's exactly what an arc welder is.

If you want sparks that look like some piece of equipment is frying itself, perhaps you could shoot closeups of a CD being destroyed by a microwave oven.

If you want simulated lightning, find a geek with a Tesla coil.

Just don't do what George Pal did for the original War of the Worlds, and use an industrial grinding wheel to generate simulated death rays. First time I ever saw his Martians mowing down the populace, my immediate reaction was "what are those things grinding? Oh, right. Cheesy low-rent death ray effect".
posted by flabdablet at 4:29 PM on March 11, 2006

Best answer: I think you might want a Spark Ejector.
posted by frogan at 4:45 PM on March 11, 2006

Rent a spark generator?
posted by ikkyu2 at 4:45 PM on March 11, 2006

I'd do this with CG. Compositing for something like sparks is going to look awful.
posted by devilsbrigade at 5:11 PM on March 11, 2006

Here's the guts of a disposable 35 mm camera having the flash capacitor shorted out with a Swiss Army knife:

posted by plinth at 5:29 PM on March 11, 2006

You could use a grinder on metal. If you did it outside or in a garage it would be safe. I'm sure an angle grinder would be easy and cheap to rent, and you can find scrap metal around anywhere.
posted by OmieWise at 5:30 PM on March 11, 2006

You can also achieve the same effect as an angle grinder on a smaller (safer, but wear goggles just in case) scale using a Dremel cutting wheel:
This may not look "electrical" enough though.
posted by Popular Ethics at 5:38 PM on March 11, 2006

You could buy an old Neon sign transformer, which will put out some seriously high potentials, as seen in many a Jacob's Ladder project.

Use real beefy connectors rated for this sort of thing, and have a quick blow fuse in line with them. Have your actor actually connect them, and they'll almost certainly arc as they bring them close together.

This is probably fairly dangerous, but it would be the most realistic option. Find an electrical engineer with experience with HV before attempting this.
posted by phrontist at 6:02 PM on March 11, 2006

(You need some sort of fuse to prevent the transformer from exploding when you make contact)
posted by phrontist at 6:03 PM on March 11, 2006

If you want to composite (I wouldn't but, hey) then I think the Neon sign transformer is the way to go. Build a jacob's ladder and shoot that, it will produce very nice lines of electrical arc.
posted by phrontist at 6:13 PM on March 11, 2006

CG sparks are tough, but particleIllusion has some really slick sparky presets. If you decide to go the the way of practical (physical) sparks, try to shoot them against a black background, which makes it much easier to comp them onto a new background plate (using the Screen transfer mode, a la After Effects or Photoshop). Screen drops black out to be transparent.
posted by dbiedny at 6:16 PM on March 11, 2006

Response by poster: Funny, I use particleIllusion all the time. Maybe it's just me, but I feel like I always can tell when it's been used in a commercial. That said, I'll give it another look.

I'm also going to look into some of the theatrical solutions, like spark ejectors.

A friend of mine just recommended some balloon squibs, flash paper, and sparkle powder. So, maybe I'll try that.

I'd love to try a jacob's ladder, but I'm afriad that I'd electrocute myself.

Finally, wouldn't the sparks from welding be the kind of thing that is so bright it might damage a camera's CCD?
posted by MattS at 9:42 PM on March 11, 2006

Have you considered iron filings thrown/fired/ejected into a hot flame?
posted by alby at 5:06 AM on March 12, 2006

Finally, wouldn't the sparks from welding be the kind of thing that is so bright it might damage a camera's CCD?

Possibly, but easy to fix -- neutral density filters. Heck, that's what weldors use so that they can look at what they are doing.

Note, with regard to the film flash cap -- be careful. Most of the disposable ones are 350uF at 300V caps -- that's a fair amount of charge, and should you discharge it into you, it'll hurt.
posted by eriko at 6:10 AM on March 12, 2006

Angle grinder is the way to go. You can buy a crappy one at Harbor Freight for $15. Grind it (the aluminium oxide disk) against pretty much any metal object and it will create a huge shower of spars.

Duct tape that sucker into the on position, brace it against something to grind on, and use a long extension cord as the remote control.

You don't want to be anywhere near this thing if it is not securely strapped down, as the cheap ones spin just as fast as good ones, but are really off-balance, so they vibrate like uh, a lot.
posted by popechunk at 8:06 AM on March 12, 2006