Another Thursday, another overlong look at some element of the tattoo stencil process. This week, we’re going to talk about the thermographic printing. As always, this is going to be fairly science heavy- the processes that undergird thermographic printers are fundamental to the cosmos itself.
To begin, lets briefly discuss the quintessential thermographic printer- the 3M Thermofax. Minnesota based 3M introduced the Thermofax in the middle part of the 20th century, and over the course of the machine’s roughly 30 year manufacturing history there were several variant models, including the Thermofax Transparency Maker. The Thermofax was a workhorse for countless schools, businesses, military bases, and prisons, as it provided an easy way to “burn” master copies for use on ethanol/methanol spirit duplicating machines. However, with the introduction of inexpensive xerographic and digital duplicating in the 1980s, many organizations began to phase out these machines. And the rest is history for tattooing, as slowly but surely more artists began adopting the technology for stencil making.
Thermographic printers use electromagnetic radiation in the infrared spectrum to “burn” stencils. And yes, that simultaneously sounds like “gee-whiz” atomic age science fiction and “GOJIRA!!!” atomic age science fiction, so lets unpack what “electromagnetic radiation” is.
Electromagnetic radiation is simply radiant energy released by electromagnetic processes. The classical description of this energy is that it travels in waves that oscillate at a defined wavelength- measured in Nanometers (nm)- though more dynamic descriptions of electromagnetic radiation articulate the complicated wave-particle duality. Human beings have developed tools to experience this radiated energy.
Human eyes have rods and cones that become excited or activated by what we describe as the “visual spectrum” of light (about 400-700 nm), but for certain wavelengths that we cannot see we have other ways of visualizing or approximating them. For example, “hard X-rays” (sub .2nm) easily penetrate living tissue, and are regularly used for examining the human body- they are commonly visualized via how they interact with radiographic plates or digital sensors. Radio waves (from 100 micrometers to 100 kilometers) are also a form of electromagnetic radiation, which human beings interact with using radio equipment like a tuner.
The huge variety of electromagnetic radiation plays a role in the complicated ways people think about “radiation” – the layman’s term more often evokes Tromaville body horror than the way your cellphone screen is projecting these words. And to be sure, some electromagnetic radiation is extremely dangerous. Cells can be damaged and die if they are exposed to certain wavelengths. But the human body (like every other physical collection of matter) also emits electromagnetic radiation- the average adult emits approximately 9 megajoules or 2000 kcal over the course of an average day, much of it in the form of infrared.
The electromagnetic radiation that Thermofax machines and other thermal copiers emit is in the infrared spectrum (somewhere between 700nm and 1mm). While the human eye cannot see in the infrared spectrum, we often experience it in the form of heat as it is absorbed and radiated off of “black bodies.” And that heat is precisely what the lovely engineers at 3M realized would be perfect for melting wax.
See, physicists have long theorized what they describe as a “Black Body.” Black bodies are objects that are perfectly absorptive of electromagnetic radiation and perfectly radiative. This idea is fundamental to thermodynamics, and physicists like Planck and Kirchoff have laws that pertain to this idealized object/state. The opposite of the black body is the “white body” and perfectly unabsorptive and unradiative object/state.
In practical terms, think about a giant parking lot. One half of the parking lot is painted black with asphalt, the other white with chalk. As the sun beats down on the parking lot, one half heats up while the other stays relatively cool. At the end of the day, one side continues to radiate heat while the other is already the same temperature as the air. From experience, we all know it is the black side of the parking lot that will be hotter- perhaps hot enough to melt the rubber on the bottom of your shoes- and it will take longer for the black side to cool off. This experience-this thought exercise – represents a universal thermodynamic constant. So, congrats, you’re a physicist.
Inside the thermofax is a giant light bulb that mostly emits infrared light. The black lines in your flash or drawing absorb this light, as the black lines approximate the idealized black body that physicists like to talk about. But the stencil paper absorbs comparatively less of the infrared radiation, meaning it doesn’t heat up nearly as much as those black lines. As the light shuts off and the energy absorbed by the black lines tends towards equilibrium, the wax most proximal to the black lines melts onto the stencil sheet. This imbalance and tendency towards thermodynamic equilibrium creates areas where the wax in the stencil melts and doesn’t melt.
And there you have it. That’s how a thermographic printer works, and how what tattoo artists do on a daily basis is a microcosm for some of the most fundamental laws of the cosmos.