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Thermal image copying is a staple of the tattoo industry.  Nearly every tattoo shop utilizes this technology for the creation of stencils, but do you know how it works?

 

Before the invention of copy machines, the reproduction of the printed word or art was a very tedious undertaking.  Scribes were employed to sit at small tables and at backless chairs hunched over manuscripts for hours a day to copy documents by hand.  The threat of Viking invasion forced monasteries to place their libraries in protected locations within the building, often requiring the scribe to climb a 20 foot ladder and then pull the ladder up behind them for safety.  The threat of fire from an open flame precluded the use of candles, so the only light by which the scribe could work was often a small window.  The job was performed in all kinds of inclement weather.

 

 

Worst of all, was the constant threat of devilish errors introduced into the copying process.  The tedium of the job resulted in mistakes, and what better scape goat than to blame Satan?  Enter Titivillus, a demon reportedly sent by Satan to induce the scribes to make mistakes.  "The Devil made me do it!" made for a good excuse back in those days.

 

Fortunately, copying devices begun to appear and made the job a whole lot easier.  Johannes Gutenburg revolutionized printing with his famous printing press in 1440.  The Gutenburg press could churn out as many as 3,600 pages in a single day compared to just a few pages a day by a medieval scribe.

 

However, this was still just print work.  The ability to take an existing document and copy it exactly was still hundreds of years away. 

 

During the 20th century, devices to directly copy materials were developed.  One of the novel inventions was the so-called Ditto Machine.  Also known as a "Spirit Duplicator", the Ditto Machine used a two-ply "spirit masters", the first of which could be drawn upon resulting in the impregnation of this paper with a colored wax (usually an aniline dye) from the second page.   The sheets were then separated and the wax-coated spirit master was then placed on a drum and a solvent was applied to this master, soaking into the colored wax.  With each turn of the drum, a portion of the colored wax is then released creating a new copy.  The downside of this process was the use of noxious alcohols such as methanol and isopropanol (hence the name "spirit" masters).

 

In the 1950's 3M improved on the process with their Thermofax technology.  This advance eliminated the need for solvents and effected the transfer of the colored wax by a leukodye reaction.  The master image could be placed against a sheet of thermally-reactive (heat activated) paper.  Infrared light from a bulb within the device is absorbed by the ink in the master image causing a leukodye reaction to occur in the thermal paper.  Since infrared light is absorbed by dark colors and reflected by light or white colors, the reaction would preferentially occur only in the portions of the thermal paper in direct apposition to the image, separating the dye from the paper coating and transferring it to the copy page.  This process has become known as direct image printing, since the original image is required to be present for each copy made.

 

Xerox changed the game again with the ability to create latent image printing, in which the master image could be held electrostatically and an unlimited number of copies could be quickly created.  The process became even more useful when the latent image could be created digitally, from a computer, so that no physical master is even needed.

 

Although thermal printing is still commonly used in such devices as cash registers and barcode printers, direct thermal copying has essentially become an ophaned technology.  Tattoo shops still love the use of thermal image copies for the use as stencils in the creation of tattoos.