Note: Prussian Blue

The German textile industry of the 19th Century was prosperous and its economic importance drove the development of many fabric dyes. Many of the stains used in histology were first invented as a way to color cloth. Since the German dye chemistry industry was so large and so much money was spent on it, it's not surprising that a great many of the famous names associated with histological structures are those of German biologists. They had access to the widest range of materials in creating their staining routines.

"Prussian Blue" is ferric ferrocyanide. It was the principal pigment of the dyes used in German army uniforms, hence the name: it was the earliest of the synthetic dyes, first being manufactured in the late 18th Century. Since the French hate to give the Germans credit for anything useful, they call it "Paris Blue," presumably because they used it in their uniforms as well. Prussian blue is still made commercially and used as a pigment in printing inks, paints, typewriter ribbons, and in carbon paper. The Prussian line infantryman in this old chromo is wearing a tunic dyed with Prussian Blue.

It's horrifying to realize that most of my students aren't old enough to remember cloth typewriter ribbons and carbon paper, and may never have seen either. But back in the infernal darkness of the B.X. (Before Xerox) era, carbon paper was a typist's only means of making copies of documents, and the worst professional trial a typist could endure.

One of my first summer jobs was as an office boy in a very large Wall Street law firm. This was in 1965, and there wasn't a single Xerox machine in the entire firm, a mammoth operation with 30-odd partners and hundreds of associates. Among my chores as a go-fer was making up "carbon sets" for the women in the typing pool. These were alternating sheets of thin typing paper and carbon paper, in packets of 3, 9, 11, or whatever number of sheets was required for a given document.

If a typist made a mistake, what she had to do was scrape the error off all of the copies with a razor blade, insert another scrap of carbon paper at the appropriate spot, and re-strike with the correct letter. Needless to say, this was a major headache, and a very strong incentive for them to become really, really accurate typists. I suspect that the day that firm bought its first Xerox copier (long after I had left) there was a party in the typing pool like unto the Feast of Nebuchadnezzar, and carbon paper fueled the bonfire.