Originally published at: https://boingboing.net/2018/06/25/watch-this-cool-demonstration.html
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I’ll stick with my Galvanic Lucifer.
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When I worked in a screen-print shop in the 70s, we still used carbon-arc lamps for exposing photo-sensitive prepped screens. You needed an ungodly bright light, but at just the right sector of the spectrum. Part of the skill was adjusting the arc distance to create the purplish cast that would indicate you were working with the needed UV band. And these units were REALLY big, probably about five feet tall and three feet wide, on wheels so you could trundle them up to the exposure frames.
Our main screen-burner guy used to strip down to cut-offs and sandals during the day, and would stand off to the side of the exposure frame wearing protective goggles whilst the screens were burned. He’s always have quite the tan, year-round.
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I used to operate some very vintage 35mm film projectors in college that used Peerless carbon arc lamp houses. Those were in fact motorized, so after you struck them and set up the gap, they were fairly hands free. They would in fact drift a bit, so you’d have to line them back up every 5-10 minutes – the light from inside the lamp house would shine up through a small opening and onto a paper card with two vertical lines | | and you’d simply rotate the two knobs to line each electrode on the lines. There was also a small viewing window made with welder’s glass for making sure the flame shape was correct.
The carbon rods themselves came in two different sizes, one for the cathode and one for the anode. The cathode rods were shorter as they burnt much slower than the anodes. They were manufactured by Union Carbide, and since most movie houses and cinema had long before switched to xenon lamp houses, they were increasingly expensive. They were jacketed in copper which melted in small droplets into a small metal pan – we collected the copper and sold it to offset the cost of the rods. We got about 2 twenty minute reel’s worth of light out of a pair of them. We’d keep the leftover ends around for standalone trailers or other kinds of short films.
It was considered bad form and cause damage to the equipment if you ended up burning a rod down to the rod holder.
Yes, we’d get that purple flame if the gap was spaced too far apart – at that point it would cause a telltale reddish flickering on the movie screen, and you’d have to run back and adjust the gap.
Here’s an old fashioned movie changeover using the same set up I worked on:
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Bit of trivia which I only know because I went to a school named after its inventor…
The arc lamp was invented by Sir Humphry Davy in a break between the miner’s safety lamp, discovering seven elements, writing poetry, burning diamonds, snorting nitrous oxide and climbing Vesuvius during eruptions. Davy noticed the luminous plasma between the two electrodes formed an arch shape because of the strong convection current - so he called it an arch light.
Somehow arch was later corrupted to arc.
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And this historical job is why even in 2018 you can find movie credits listing ‘lamp operator’ in the electrical department.
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The picture of the colorful patterns is not the carbon arc lamp by the way. A carbon arc lamp doesn’t make colorful patterns, it just makes a ton of bright white light.
The BB summary is a bit confusing and makes it seem as if the picture of the colorful string is a carbon arc lamp.
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