X-Rays Mine Antique “Locked Letter,” Prompting Look at X-Ray Tech

300-year-old correspondence folded into locked position read with x-ray machines

By Jonny Lupsha, Wondrium Staff Writer

X-rays were recently used to read a letter that was folded and locked shut. The 300-year-old correspondence gave up its secrets without being broken thanks to hyper-sensitive scanning equipment. X-ray tech uses atomic electrons for its imagery.

Xray machine close up
X-ray machines produce a stream of electromagnetic radiation that is focused on a particular area of the body, sending an image of internal structures to a computer. Photo By Doro Guzenda / Shutterstock

Scientists recently discovered a new use for X-ray imaging technology: reading the contents of a 300-year-old “locked letter.” Before sealable envelopes were widely available, writers of correspondence often folded their letters into intricate patterns, “locking them” closed, to only be opened through secret methods.

Curators of these letters who couldn’t solve their puzzles faced a dilemma that has lasted centuries: either leave the beautiful folded pages intact and let the letters remain unread or open them by force, damaging them in the process. Some very sensitive and very fine-tuned X-ray technology has enabled scientists to read such a locked letter by imaging traces of metal in the ink used to write it.

How does X-ray tech work? In his video series Physics in Your Life, Dr. Richard Wolfson, the Benjamin F. Wissler Professor of Physics at Middlebury College, said that wavelengths and frequencies are at the heart of reading and making electromagnetic waves, from radio waves to gamma rays.

Keep It Off My Wave

“An electromagnetic wave […] is a wave in which the disturbance is at right angles to the direction in which the wave is going,” Dr. Wolfson said. “There’s an electric field and there’s a magnetic field; they, themselves, are at right angles to each other. They are in phase in the sense that each peaks at the same point, and they’re both at right angles to the direction the wave is going in.”

According to Dr. Wolfson, electromagnetic waves can be characterized by their wavelengths and their frequencies. He also said there’s no clear or sharp distinction between the wavelengths—microwaves, for example, are simply a higher frequency than radio and TV wavelengths. Microwaves merge into infrared, which merges into the visible. Ultraviolet, X-rays, and gamma rays follow, respectively. How are they made?

“The way you make electromagnetic waves is to take either an electric charge and wave it around, or a magnet and wave it around in some kind of accelerated motion,” Dr. Wolfson said. “That’s all it takes—accelerating an electric charge with a magnet makes electromagnetic waves.”

X” Marks the Spot

“For instance, visible light is produced primarily by atoms, which are pretty small; X-rays are produced by inner electrons of atoms, mostly,” Dr. Wolfson said. “Gamma rays are produced by atomic nuclei; infrared is emitted primarily by molecules, and so on.”

Dr. Wolfson said that X-ray machines work by accelerating electrons in a special tube, which then gets slammed suddenly and very hard into a target made of tungsten. The sudden stop represents a very rapid acceleration which happens so quickly it produces electromagnetic waves. .

“What happens is that we have an electron gun at one end of this device, a tungsten target at the other end, you blast that electron beam out, it hits the target, comes to a stop, and out come X-rays at the bottom of the tube,” Dr. Wolfson said. “When you go to the dentist or doctor and get X-rayed, they are sent through you, and on to some kind of film or electronic detector.”

Thankfully, scientists revealed the secrets of the locked letter without having to hold it up to their mouths during a dental exam. If they did, depending on the contents of the letter, it may give new meaning to the phrase, “Lying through your teeth.”

Edited by Angela Shoemaker, Wondrium Daily