Editing Spark printing (section)

{{for|the process which uses heat and white thermo paper|thermal printing}}
{{History of printing}}

[[File:Sinclair.zx.thermal.printer.jpg|thumb|The Sinclair ZX Printer, a small spark printer for the ZX81 and ZX Spectrum computers]]

'''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 [[Pulse (signal processing)|pulse]]s of [[electric current]] to burn away spots of the conductive layer.  Typically, one or more [[electrode]]s are swept across the page perpendicular to the direction of paper motion to form a [[Raster scan|raster]] of potential burnt spots.

[[Western Union]] developed the paper for this printing technology in the late 1940s, under the trademark "[[Teledeltos]]".<ref>Grosvenor Hotchkiss, [http://massis.lcs.mit.edu/archives/technical/western-union-tech-review/03-1/p006.htm Electrosensitive Recording Paper for Facsimile Telegraph Apparatus and Graphic Chart Instruments], [http://massis.lcs.mit.edu/archives/technical/western-union-tech-review/03-1/readpg.htm Western Union Technical Review, Vol. 3, No, 1] (January 1949); page 6.</ref>  The Western Union "Deskfax" [[fax machine]], announced in 1948, was one of the first printers to use this technology.<ref>G. H. Ridings, [http://massis.lcs.mit.edu/archives/technical/western-union-tech-review/03-1/p017.htm A Facsimile transceiver for Pickup and Delivery of Telegrams], [http://massis.lcs.mit.edu/archives/technical/western-union-tech-review/03-1/readpg.htm Western Union Technical Review, Vol. 3, No, 1] (January 1949); page 6.</ref>

Spark printing was a simple and inexpensive technology. The print quality was relatively poor, but at a time when conventional printers cost hundreds of [[Pound sterling|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.<ref>{{cite web |author1=Paper Loop Consumables |title=Electrosensitive Paper Roll 60mm wide x 34mm diameter x 12.7mm core |url=https://www.paperloop.co.uk/products/Electrosensitive-Paper-Roll-60mm-wide-x-34mm-diameter-x-12.7mm-core.html |date=2020-03-29}}</ref>