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History of printing
Techniques Woodblock printing 200 Movable type 1040 Intaglio (printmaking) 1430 Printing press c. 1440 Etching c. 1515 Mezzotint 1642 Relief printing 1690 Aquatint 1772 Lithography 1796 Chromolithography 1837 Rotary press 1843 Hectograph 1860 Offset printing 1875 Hot metal typesetting 1884 Mimeograph 1885 Daisy wheel printing 1889 Photostat and rectigraph 1907 Screen printing 1911 Spirit duplicator 1923 Dot matrix printing 1925 Xerography 1938 Spark printing 1940 Phototypesetting 1949 Inkjet printing 1950 Dye-sublimation 1957 Laser printing 1969 Thermal printing c. 1972 Solid ink printing 1972 Thermal-transfer printing 1981 3D printing 1986 Digital printing 1991
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Spark printing is an obsolete form of computer printing and before that fax and chart recorder printing which uses a special paper coated with a conductive layer over a contrasting backing, originally black carbon over white paper but later aluminium over black paper. Printing on this paper uses pulses of electric current to burn away spots of the conductive layer. Typically, one or more electrodes are swept across the page perpendicular to the direction of paper motion to form a raster of potential burnt spots.

Western Union developed the paper for this printing technology in the late 1940s, under the trademark "Teledeltos". The Western Union "Deskfax" fax machine, announced in 1948, was one of the first printers to use this technology.

Spark printing was a simple and inexpensive technology. The print quality was relatively poor, but at a time when conventional printers cost hundreds of pounds, spark printers' sub-£100 price was a major selling point. The other major downside is that they can only print onto special metallised paper and such an electrosensitive paper is no longer widely available, but is still sold as of 2020.

Models

By 1979, the Comprint 912 was widely advertised as being faster, quieter, and less expensive than competitive matrix printers, with its "special aluminized 'silver paper'" being superior to ordinary paper, and "on those rare occasions when you really do need a plain bond paper copy, just run your Comprint 912 printout through your plain bond copy machine and you've got it."

The Sinclair ZX Printer, introduced in November 1981 for the low-end ZX81 (and later for the ZX Spectrum) home computers used the spark printing method, and retailed for £49.95.

In the early 1980s, Casio released a "Mini Electro Printer", the FP-10 for some of their scientific calculators. It used Casio CMP-36x5 paper.

The Hewlett Packard 9120A, which attached to the top of the HP-9100A/B calculator, also used the sparking technique.

Tandy / Radio Shack TRS-80 Screen Printer, Quick Printer, and Quick Printer II all used this same method and special paper.

The Sharp Corporation ELSIMATE EL-8151 portable calculator had a built in spark printer which used silver-colored paper. It is known to be compatible with the Casio CMP-36x5 paper used by the FP-10, despite the Casio paper having a slightly larger core diameter.

Variants

A different spark printer implementation propelled dry toner from a tiny hole in the end of a glass rod, using a high-voltage spark between the platen and print head. The glass toner rod held a solid mass of toner, pushed toward the ejection tip by a spring. This had the advantage of printing onto plain paper, but the disadvantage of the toner not being cured to the paper, and thus easily smudged. Similar to the Sinclair printer, this printer had only one stylus (the toner rod), since the entire plate behind the paper served as the other spark electrode. The printer could only print one line of pixels at a time.

References

1. Grosvenor Hotchkiss, Electrosensitive Recording Paper for Facsimile Telegraph Apparatus and Graphic Chart Instruments, Western Union Technical Review, Vol. 3, No, 1 (January 1949); page 6.
2. G. H. Ridings, A Facsimile transceiver for Pickup and Delivery of Telegrams, Western Union Technical Review, Vol. 3, No, 1 (January 1949); page 6.
3. Paper Loop Consumables (2020-03-29). "Electrosensitive Paper Roll 60mm wide x 34mm diameter x 12.7mm core".
4. "Comprint advertisement". Computerworld. 8 October 1979. Retrieved 13 September 2020.
5. "Casio FX-702P". Computer Museum. Retrieved 2006-11-30.

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