colmascope

plural colmascopes

1. An instrument for visualising stressed regions, especially internal regions, in substances such as glass, by detecting differences in the degree of rotation of the plane of polarisation, generally by placing the object between crossed polarizers.

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   A device like those in which one polariser is fixed and the other rotatable — often with marked gradations — is called a polariscope or a polarimeter. One in which the polarisers are fixed at right angles is often called a "colmascope", but this name is actually a trademarked device, first registered by American Optical company... the trademark has lapsed effective 1997. The term "colmascope" has suffered the same fate as Kleenex and cellophane, shifting from trademark to generic name. I still see old Colmascopes in labs and workshops... Why did American Optical come up with the name "Colmascope" …? Certainly they wanted a name that would set their device apart from the other polariscopes on the market, so they cast about for something without "polari-" in the name. Their choice seems to derive from Greek root kolmo- meaning "perpendicular", since it has the two axes of polarisation of the two polarizers set immovably perpendicular to each other.

   Stephen R. Wilk (2021), Sandbows and Black Lights, pages 47–