Rubylith is a brand of masking

Photomask

A photomask is an opaque plate with holes or transparencies that allow light to shine through in a defined pattern. They are commonly used in photolithography.-Overview:...

 film, invented and trademarked by the Ulano Corporation. Today the brand has become genericized

Genericized trademark

A genericized trademark is a trademark or brand name that has become the colloquial or generic description for, or synonymous with, a general class of product or service, rather than as an indicator of source or affiliation as intended by the trademark's holder...

 to the point that it has become synonymous with all coloured masking films.

Rubylith consists of two films sandwiched together. The bottom layer is a clear polyester

Polyester

Polyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate...

 backing sheet. The top layer is a translucent, red coloured, self adhesive emulsion

Emulsion

An emulsion is a mixture of two or more liquids that are normally immiscible . Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion is used when both the dispersed and the...

. It is designed to be both easy to cut with a knife and light safe for use with orthochromatic

Orthochromatic

- Orthochromatic photography :Orthochromatic photography refers to a photographic emulsion that is sensitive to only blue and green light, and thus can be processed with a red safelight. The increased blue sensitivity causes blue objects to appear lighter and red ones darker...

 films.

Rubylith is used in many areas of graphic design

Graphic design

Graphic design is a creative process – most often involving a client and a designer and usually completed in conjunction with producers of form – undertaken in order to convey a specific message to a targeted audience...

, typically to produce masks for various printing techniques. For example it is often used to mask off areas of a design when using a photoresist

Photoresist

A photoresist is a light-sensitive material used in several industrial processes, such as photolithography and photoengraving to form a patterned coating on a surface.-Tone:Photoresists are classified into two groups: positive resists and negative resists....

 to produce printing plates for offset lithography or gravure. It is also frequently used during screen-printing

Screen-printing

Screen printing is a printing technique that uses a woven mesh to support an ink-blocking stencil. The attached stencil forms open areas of mesh that transfer ink or other printable materials which can be pressed through the mesh as a sharp-edged image onto a substrate...

.

Ulano also produces a yellow coloured, masking film called Amberlith, that is not light safe but easier to use for masking when not employing a photoresist.

The physical layouts of the first generations of Intel microprocessors (at least the Intel 4004

Intel 4004

The Intel 4004 was a 4-bit central processing unit released by Intel Corporation in 1971. It was the first complete CPU on one chip, and also the first commercially available microprocessor...

, 4040

Intel 4040

The Intel 4040 microprocessor was the successor to the Intel 4004. It was introduced in 1974. The 4040 employed a 10 μm silicon gate enhancement load PMOS technology, was made up of 3,000 transistors and could execute approximately 60,000 instructions per second.- Extensions :*Instruction Set...

, 8008, 8080, 8085, and 8086) were designed by physically cutting sheets of Rubylith into thin strips to lay out the circuits to be printed, a process made virtually obsolete by current computer graphic design capabilities.