Sunday, June 10, 2018




It's Judy Garland's birthday.

Now, some behind-the-scenes images of the making of The Wizard of Oz and some pedantry on my part:

Film is made of celluloid. Silver nitrate (later, silver halide) on the film is what reacts to light, creating an image. If the silver nitrate is big-grained, it reacts fast to light ("faster film", or "higher ISO rated film"). But the image can be grainy. If the silver nitrate is ground much more finely, it reacts much slower to light ("slower film" or "lower ISO rated film"). But you get a much clearer image.

The way to overcome this is by flooding the image with immense amounts of light. To the human eye, a scene might appear washed-out. But because slow film is not as good as the human eye, it will turn out just right.


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Color film works the same way. Technicolor (which was how The Wizard of Oz was filmed) used a prism to split the light into three beams. One beam of light hit a strip of film highly sensitive to green light. One beam of light hit a strip of film highly sensitive to red, and another to film sensitive to blue.

Splitting the light like that required even more light to be poured onto the set.

When silver halide reacts to light, it actually changes physical form. Looking at a piece of film closely, you can see it looks like a series of peaks, valleys, canyons, and plains. By running the green film through some green dye, the dye fills in those areas meant to be green (because they are deeper). Ditto for the other two colors.

Originally, the three dyed films were cemented together, but this caused huge problems when run through a hot projector. The films "cupped" and warped, and that was bad.


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In 1928, Technicolor invented the dye-transfer process. A piece of gelatin-coated film was pressed against each of the dye-covered color films. This transferred the dye to the gelatin. When developed, the gelatin was coated and hardened so that it retained the dyes. Expose the gelatin to a black-and-white image (at 50 percent light), and you got a really sharp image.

The dye-transfer process required tremendous precision. A tiny frame of film was blown up of thousands of times on screens, and even the slightest error would show up.

Adding successive layers of dye darkened the film, of course, as light had to pass through five layers (three dyes, a B&W, and the celluoid). The process was improved by using "subtractive" color. Instead of adding red, for example, to green and blue, why not subtract (block) red from the full spectrum of color? This would allow the blue and green to come out. Do that for each color (red, blue, green), and you'd get a much thinner layer of dye. Technicolor figured out that the "blue record" should take yellow dye, the red record a cyan dye, and the green record a magenta dye. Blocking color required a lot less dye than adding color.


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How much light was needed to light the sets of The Wizard of Oz? At the time, Hollywood used a measurement call the foot-candle (fc). To give you an idea of the scale, full sunlight is approximately 10,000 fc, while an overcast day is about 100 fc. A well-lit home has lighting of 5 to 40 fc. An office space has lighting of about about 70 to 90 fc, although visually intensive work (like surgery, graphic arts, and electronics work) usually requires 200 fc.

On The Wizard of Oz, Technicolor required 500 to 600 fc for well-lit scenes like Munchkinland. (This was down from the 800 fc used just a few years earlier.) Darker scenes, such as the interior of the Wizard's palace, the Wicked Witch's home, or the Dark Forest, could be shot at 400 fc or slightly less.

To achieve this high intensity of light, arc lamps were used. (These are bigger, hotter, and less intense than today's arc lights.) A total of 150 arc lamps were needed. MGM used every single arc lamp it owned, and borrowed every available arc lamp from every other studio in town. Lighting costs alone totaled more than $225,000 of the film's $2.77 million budget.


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How hot is a set lit with 150 arc lamps, producing 600 fc?

Temperatures on the soundstage were routinely in the high 80s and low 90s. Temperatures could sometimes reach 100 degrees F.

There was no air conditioning. The doors of the soundstage would be flung open as soon as filming stopped. Massive fans would be rushed in front of the open doors to try to cool things down.

It was common for extras (who had to remain in place under the lights) to faint from the heat. A fire inspector was on the set during brightly-lit scenes to look for hot spots, smoke, or other problems. Eyestrain among the cast was common. Some actors could only keep their eyes open for three or four minutes before having to get out of the light.

The arc lamps could only run for 30 minutes before they burned up the carbon filaments. A small army of lighting technicians was working the set, constantly nursing the lights and replacing filaments.

Everything on the set was darker than you might expect. Costumes, props, buildings, trees, the Yellow Brick Road: They were all dull and smoky looking. The Ruby Slippers were actually dark burgundy, and only looked ruby-red on film because of the powerful lighting. Sets were constantly checked, because the high-intensity lights made colors fade fast.

Just a year later, improvements to Technicolor would allow films to drop the lighting to 200 to 300 fc. (That's the lighting used on Gone With The Wind.)


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