Operating heavy machinery that's nearly twice her height in a cotton mill in Lancaster, South Carolina, in 1908.

She was just one of many children working in mills, fields, factories, and mines.

And although these kids were spread across the United States, working in separate industries, they all had one thing in common.

They all met Lewis Hine.

At the turn of the 20th century, the United States knew it had a child labor problem.

The 1900 federal census revealed that 1.75 million children under the age of 16, more than one in five, were working at this time.

The Industrial Revolution had mechanized American and European manufacturing, and a cheap labor force was needed to complete repetitive tasks for hours on end.

Children from poor families were targeted for these jobs because they would work for next to nothing and were less likely to strike than adults　

State legislatures and the American public knew this was happening on a mass scale, but didn't act.

Until they saw what it actually looked like.

Starting in 1908, the newly formed National Child Labor Committee hired a photographer to investigate and report on the industries employing children.

That photographer was Lewis Wickes Hine: educator, sociologist, and member of the Progressive Movement.

A period in the United States that saw a wave of political activism and social reform.

Hine emphasized the potential power of photography as a tool for social reform in a speech he gave in 1909 called "Social photography: how the camera may help."

He said, The dictum, then, of the social worker is "Let there be light;" and in this campaign for light we have for our advance agent the light-writer — the photograph.

He traveled extensively, gathering information, interviews, and images of working children across the country.

He visited coal mines in Pennsylvania.

Where adolescent "breaker boys" worked underground for hours, separating impurities from coal.

Sardine cutters in Maine.

Oyster shuckers in Louisiana, some as young as 4 years old.

Tobacco pickers in Kentucky.

Cranberry pickers in Massachusetts.

Beet farms in Colorado.

And young messengers and newsboys in cities all over the country.

Many of the photos captured adults nearby, supervising the children as they worked.

When Hine wasn't allowed access to the mills and factories, he waited outside and documented the comings and goings of its workers, whose shifts often lasted late into the night.

Laborers would pose for portraits and tell Hine a bit about themselves, their wages, and their work conditions.

Sometimes they showed their horrific injuries and described what happened.

Like this boy from Bessemer City, North Carolina, whose hand got crushed in the gears of a cotton spinner.

We know that because each photo, numbering over 5,000, includes a detailed caption written by Hine.

Hine coined the term "photo stories" to describe this marriage of images and text.

And it's a big part of how the photos humanized the lives of child laborers to an indifferent public.

But it's also his photographic technique that makes them feel so personal.

Let's use the photos of cotton mill workers like Sadie as an example.

First, many of these photos are framed the exact same way, just substituting a different worker.

Hine was trying to show that each child's experience was part of a widespread problem, and the repetition in the images signals that.

You can really see how intentional the framing is when you look at how the image of Sadie appeared when it was first published in a Progressive magazine, in 1909.

It's opposite a nearly identical photo of a different worker, set so that the symmetry of the two images makes the machinery seem to go on and on.

The left-hand caption says, "Spinner. A type of many in the mill."

Hine's photographs are also shot with a very shallow depth of field, which basically means a narrow part of the photo is in focus, and the rest is blurred out.

A photo with a deep depth of field would look like this one by Jacob Riis, who was photographing New York City slums around the same time.

Notice how the playground in the background is in focus, just like the kids in the foreground.

Now look at Hine's portraits.

In this one, the factory this boy works at looms behind him, but it's almost totally blurred out.

This was a recurring visual theme — to include the machinery or the workplace in the frame, but obscure it, favoring the worker instead.

This narrow point of focus, combined with shooting from a lower angle.

The eye level of these children is why these images are so effective at humanizing their subjects.

Photos like the ones from the South Carolina cotton mills changed the public perception of child labor in the United States,

Ultimately pressuring state legislatures to introduce laws regulating work for those under the age of 18 and sending kids back to school.

Lewis Hine went on to photograph the construction of the Empire State Building in New York City, using the same dignifying techniques he photographed child laborers with.

Considering the perspective of his subjects with a narrow focus, emphasizing the worker, not the machinery.

Hine was one of the first to use a camera as a tool for social documentary, to shine a light on the mostly unseen.

He understood early on the power images have to tell stories.

As he said in that 1909 speech: Take the photograph of a tiny spinner in a Carolina cotton mill.

With a picture thus, sympathetically interpreted, what a lever we have for the social uplift.

Hey everyone, that was Darkroom season 1!

I'm going to take a break from it and work on some other stuff, like History Club with Phil.

If there are photos you think would make good stories for the next season, make sure to leave a comment below.

In the meantime, if you're looking for more great videos on photography in history, check out the documentary "The Man Who Shot Tutankhamun", available on CuriosityStream.

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