Carbon tissue is a gelatin-based emulsion used as a

photoresist A photoresist (also known simply as a resist) is a light-sensitive material used in several processes, such as photolithography and photoengraving, to form a patterned coating on a surface. This process is crucial in the electronics industry. T ...

in the chemical etching (

photoengraving Photoengraving is a process that uses a light-sensitive photoresist applied to the surface to be engraved to create a mask that protects some areas during a subsequent operation which etches, dissolves, or otherwise removes some or all of the ma ...

) of gravure cylinders for printing. This was introduced by

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physicist A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate cau ...

and

chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a graduated scientist trained in the study of chemistry, or an officially enrolled student in the field. Chemists study the composition of ...

Joseph Swan Sir Joseph Wilson Swan Fellow of the Royal Society, FRS (31 October 1828 – 27 May 1914) was an English physicist, chemist, and inventor. He is known as an independent early developer of a successful incandescent light bulb, and is respon ...

in 1864. It has been used in photographic reproduction since the early days of photography. Carbon materials marketing began in 1866 by

which he subsequently sold to the Autotype Company in 1868. His ready-made tissues were in three colours black, sepia and purple-brown. This method was used in Europe and USA throughout the 19th century and well into the 20th. This market was almost closed in the 1950s although some companies produce small amount of carbon tissue and transfer papers for monochrome and three-color work until around 1990

Method

The gelatinous emulsion is applied to a paper backing, and is rendered sensitive to light when immersed in a 3:4% solution of

potassium bichromate Potassium dichromate is the inorganic compound with the formula . An orange solid, it is used in diverse laboratory and industrial applications. As with all hexavalent chromium compounds, it is chronically harmful to health. It is a crystalline ...

. After drying, it is ready for use. The carbon tissue is first exposed to a film positive. In those areas where the carbon tissue has received the most light (i.e., non-image areas and highlights) the emulsion becomes thick and hard, and the thickness and hardness decreases with decreasing exposure to the light source, the emulsion being thinnest and softest in image areas corresponding to shadows and solids. After developing the carbon tissue, it is adhered to the surface of the copper-plated cylinder. A solution of

ferric chloride Iron(III) chloride describes the inorganic compounds with the formula (H2O)x. Also called ferric chloride, these compounds are some of the most important and commonplace compounds of iron. They are available both in anhydrous and in hydrated f ...

etchant is applied to the surface of the cylinder, where it eats away the copper through the carbon tissue. In the highly exposed areas, where the carbon tissue photoresist is thickest and hardest, the etchant takes a long time to eat through the hard emulsion, while in the least exposed, thinnest regions the etchant eats through the resist into the copper very quickly. Thus, in a given period of etching, the cells etched into the copper will be deepest (and thus will print the darkest) in those regions where the etchant has eaten through the quickest, while the cells etched into the copper will be the shallowest (and thus print the lightest) in those regions where the etchant has eaten through the slowest.

Usage

Carbon tissue resists were the first chemical etching media, but have been replaced by photopolymers, and chemical etching as a whole is being increasingly replaced by electromechanical engraving and computer-to-cylinder laser-cutting processes. (See Gravure Engraving.) Carbon tissue resists have also been used extensively for the manufacture of photostencils in

screen printing Screen printing is a printing technique where a mesh is used to transfer ink (or dye) onto a substrate, except in areas made impermeable to the ink by a blocking stencil. A blade or squeegee is moved across the screen in a "flood stroke ...

References

{{reflist Photographic processes dating from the 19th century History of photography 19th-century photography

Method

Usage

See also

References