Well, let's start with the technique. Ol' Serge took color photos with the three-color process - working on the principle that if you had a red image, a green image, and a blue image, you could combine them to form a full-color composite. To accomplish this he took the same photo three times on three different photographic plates, each with a different colored filter on it. He had a specially modified camera that would take the first picture, slide down the next plate, and then repeat once more for the third plate. Then he'd develop all three plates and project them all at the same time to show the color.

This produced, as you've seen, enormously detailed color photos that, with the benefit of the Library of Congress' modern retouching, look as good as images captured today. The Lumiere brothers produced a method around the same time of capturing color in one exposure, but it was a grainy and muted color compared to Sergey's. Other photographers, however, would balk at the accusation that nobody else was using the three-color method. Its principles were over forty years old at the time, and the three-color process was used to great effect in advertisements. Adolf Miethe was a German chemist-photographer who is quite obscure now, but some excellent reproductions survive of marvelous three-color portraits he shot around 1903.

Sergey had the enormous advantage of government funding. We're talking practically unlimited travel and photography resources, which made a world of difference for this task. The specialized equipment needed to be custom-built, and of course each photograph cost at least three times as much as normal in terms of raw materials. It simply wasn't worth it for most people to take pictures of things happening around them with the three-color process, and so it was reserved for studio and experimental work. Sergey's collection remained well preserved and was transferred into the capable hands of the Library of Congress, who curated and restored the images to the excellent standard we see today.