Electrostatic Printing

History

The underlying phenomenon, forming a visible image from a deposited electrostatic charge pattern on an insulating surface, traces to Georg Christoph Lichtenberg in the late 1770s. His "Lichtenberg figures" demonstrated dust adhering to charged dielectric patterns. Wikipedia's electrophotography article explicitly contrasts Chester Carlson's later light-based invention with "the dry electrostatic printing process invented by Georg Christoph Lichtenberg in 1778," while more authoritative sources, including the American Physical Society and Wikipedia's own Lichtenberg-figure article, place the discovery and its published memoir in 1777. Either way, this is a documented conceptual ancestor, not a claim that a printer existed in the 18th century.

Practical electrographic recording on dielectric or coated paper using energized styli developed through the mid-20th century, with the patent and technical literature describing electrical recording "by the direct route by means of an electrode in the form of a stylus." By the computing era this matured into commercial raster printer/plotters: Wikipedia's electrostatic-plotter article states that by 1967 several manufacturers were commercially supplying electrostatic plotters.

Versatec became a leading vendor. A Versatec Model 800 plotter dated 1970 is held in the Computer History Museum collection, where it is described as an early commercially successful electrostatic writing technique producing information on paper directly from digital data sources. Versatec was later acquired by Xerox and exhibited as "Versatec Inc., A Xerox Company." (The exact founding year and acquisition year are not firmly documented in the authoritative sources consulted, so they are not stated here.)

No single inventor should be credited for "the electrostatic printer." The concept is attributed to Lichtenberg; the commercial raster plotter was developed by multiple firms in the 1960s. Any single-name attribution should be treated as debatable.

How it works

The documented physical process has four stages:

• Special paper. The medium is dielectric-coated paper: a conductive (or made-conductive) paper base carrying a thin, highly resistive dielectric top coating that can hold a localized static charge.
• Charge writing (imaging). The paper moves past a fixed, closely spaced row of styli or nibs (tiny wire electrodes). Individual styli are pulsed on and off, depositing a dot pattern of electrostatic charge onto the dielectric surface where an image element is required. The stylus pitch sets the horizontal resolution, and paper motion builds the raster line by line.
• Toning (developing). The charged sheet passes a toner supply. In the classic Versatec-style machines this is a liquid toner (very fine pigment particles suspended in a carrier fluid), whose charged particles are electrostatically attracted to the charged dots. Dry-toner variants also existed, using a process resembling xerographic development but, as Wikipedia notes, without a transfer drum, since the paper itself is the imaging surface.
• Fixing (fusing). The toner is fixed to the paper, by evaporating the liquid carrier and/or by heat from a fuser, producing the permanent hard copy.

The key architectural point is that, unlike a photocopier or laser printer, there is no photoreceptor and no light. The image originates as an electrical signal driving the styli, and in most electrostatic plotters there is no intermediate drum: the charge is written straight onto the final sheet.

Evolution

Early machines were monochrome raster printer/plotters used to turn computer data and vector drawings (via a raster image processor) into hard copy.

Width and resolution grew over time. Versatec and Varian-class machines commonly wrote at around 200 dpi, with later models reaching 400 dpi, in widths ranging from small desktop sizes up to 72 inches, according to the ACM SIGGRAPH history archive. The Versatec 8272, described in a 1978 Information Display article from the Society for Information Display, was promoted as an exceptionally wide, high-resolution unit; its title and abstract cite a large fixed nib array (14,336 nibs) producing 200-dpi output across a 72-inch web, enabling plots up to about six feet wide. (The full article is paywalled; these figures come from its title and abstract.)

Color electrostatic plotters followed, laying down multiple toner passes. The lineage then merged into large-format laser and LED electrophotographic printers, which use a photoconductor and a charged drum rather than direct styli. As a result, the direct-charge method faded even where the "electrostatic" label persisted.

Advantages

The documented advantages of electrostatic printing are qualitative:

• Plot time independent of image complexity. Because output is rasterized, a dense, detailed drawing takes essentially the same time as a sparse one, a major practical edge over pen plotters, which slow down as the number of lines rises.
• High throughput at large size. The technology suited high-speed production of very wide plots (up to about six feet), which is why it dominated engineering, CAD, and mapping hardcopy.
• No moving pen or carriage over the media for imaging. The writing head is a fixed array, mechanically simpler for wide widths than a traversing pen.
• Economy at scale relative to pen plotting for high-volume shops, cited as a reason the technology remained useful despite early quality limits.

Disadvantages

The documented drawbacks are likewise qualitative:

• Requires special dielectric-coated paper, not plain paper, raising consumable cost and dependence. The coated media and toner were central to the business model.
• Lower initial image quality than pen plotters when the technology was young.
• Wet-process handling in liquid-toner machines: toner fluid, carrier evaporation, and associated maintenance issues are characteristic of these direct-charge families. (The closely related zinc-oxide coated-paper machines were noted for a kerosene-like odor from carrier evaporation.)
• Superseded on cost and quality by large-format inkjet, which prints on plain, uncoated media.

No specific speed, resolution, or price comparisons are asserted beyond what named sources documented for named models.

Modern use

Direct stylus-on-dielectric-paper electrostatic plotting is largely obsolete. Its wide-format engineering role collapsed after large-format inkjet plotters, such as the HP DesignJet family, arrived in the early 1990s, and it was further eclipsed by large-format laser and LED electrophotographic printers.

Wikipedia notes that surviving electrostatic color plotting remains mainly in the short-run graphics industry, printing on various paper and plastic-film surfaces. The general term "electrostatic" now most often refers to laser and LED electrophotographic devices, which are a different, photoconductor-based technology.

Relationship to other technologies

• Versus electrophotography / xerography (laser printers, copiers). Both ultimately use electrostatic attraction of toner. The decisive difference is image formation: xerography (Chester Carlson, US Patent 2,297,691, granted October 6, 1942) charges a photoconductor uniformly and then uses light to discharge selected areas, forming a latent image later transferred to plain paper. Direct electrostatic printing writes the charge image electrically via styli straight onto dielectric paper, with no light, no photoconductor, and usually no transfer drum. In effect, xerography is electrostatic printing combined with photography; direct electrostatic printing is the electrostatic half without the photography.
• Versus Electrofax (zinc-oxide coated-paper process, RCA, early 1950s). Often grouped with "electrostatic" coated-paper processes, but Electrofax paper is photoconductive: a zinc-oxide coating is charged and then exposed to light. It is therefore a direct-on-coated-paper electrophotographic process, not the stylus-charged dielectric method that is this page's subject.
• Versus pen plotters. A direct competitor for engineering hardcopy. Electrostatic won on speed and complexity but lost the low end on media cost and early image quality until inkjet ended the contest.
• Versus inkjet. Inkjet's plain-paper capability and quality drove electrostatic plotters out of the wide-format market in the 1990s.

Relationship to manufacturers

• Versatec (later Versatec, a Xerox Company) is described as a leading manufacturer of electrostatic plotting equipment, with a broad line of monochrome and color plotters at roughly 200 to 400 dpi and widths up to 72 inches.
• Xerox owned Versatec by the early 1980s and was also the pioneer of the photoconductor-based electrophotographic branch (the Xerox 914, 1959), which is the sibling technology, not this one.
• Varian was associated with electrostatic printer/plotter development alongside Versatec, fielding narrow and wide monochrome units in the mid-1970s.
• CalComp, better known for pen plotters, also offered color electrostatic plotters, such as the documented CalComp 68436.
• Hewlett-Packard is a documented reference point as the pen-plotter leader and later, via DesignJet inkjet, the disruptor of the electrostatic plotter market.
• RCA is associated with the related zinc-oxide coated-paper (Electrofax) process, a distinct but frequently cross-referenced coated-paper line.

Related printer families

Documented product-line names tied to this technology include:

• Versatec Model 800 (1970; Computer History Museum collection).
• Versatec V-80 desktop electrostatic printer/plotter.
• Versatec 8272 wide-format electrostatic plotter (1978 Information Display article).
• Versatec ACRIS / IMPRES 500 systems (SIGGRAPH history archive listing).
• CalComp 68436 color electrostatic plotter.
• HP 7600 series electrostatic plotters (HP Computer Museum).
• Electrofax (RCA), a related zinc-oxide coated-paper family, cross-referenced but photoconductive rather than stylus-charged.

Timeline

1. 1777–1778

   Georg Christoph Lichtenberg demonstrates images from deposited electrostatic charge (Lichtenberg figures), the conceptual origin cited for dry electrostatic printing. (Authoritative sources favor 1777; one widely quoted source gives 1778.)

2. 1930s–1942

   Chester Carlson develops and patents xerography (US 2,297,691, granted 1942), the photoconductor-based branch and a contextual sibling, not this technology.

3. early 1950s

   RCA develops Electrofax, a zinc-oxide coated-paper process, a related coated-paper method.

4. 1959

   the Xerox 914 makes photoconductor xerography practical (context).

5. by 1967

   several manufacturers commercially supply electrostatic plotters.

6. 1970

   the Versatec Model 800 electrostatic plotter (Computer History Museum-dated).

7. mid-1970s

   Versatec and Varian ship narrow- and wide-body monochrome electrostatic printer/plotters at around 200 dpi.

8. 1978

   the Versatec 8272 wide-format electrostatic plotter is documented in Information Display.

9. by early 1980s

   Versatec is a Xerox company; color electrostatic plotters are widespread in CAD and mapping.

10. early 1990s

    large-format inkjet (HP DesignJet) arrives, the electrostatic plotter market collapses, and the role migrates to large-format laser and LED electrophotographic printers.