The Barons Rayleigh and Corning UV Glass

The last post discussed early UV-VIS spectrophotometers. Those systems required phototubes with envelopes that pass UV. Corning’s ( Corex ultraviolet transmitting glass fit the bill and found application.

Apparently, there is another feature of Corex, although the author does not state exactly which material he studied:

Double Refracting Structure of Corex Glass

Nature, Volume 126, p. 845 (29 November 1930)

Some years ago I found that silica glass showed a doubly refracting structure (Proc. Roy. Soc., A, vol. 98, p. 284; 1920. Also Proc. Optical Convention, Part I, p. 41; 1926). This structure is quite distinct from any due to bad annealing, and seems kindred to the ‘liquid crystals’ of Lehmann. Nothing of the kind could be found in the ordinary glasses consisting of silica with metallic oxides.

I now find that the ultra-violet transmitting Corex glass of the Corning Co. shows a similar structure. This glass is said to consist in the main of calcium phosphate, though I have not seen an analysis. The subject evidently requires detailed examination, which I hope to make as opportunity allows.

(Robert John Strutt, 4th Baron) Rayleigh
Terling Place, Chelmsford,
Nov. 14.

This Lord Rayleigh is the eldest son of TheLord Rayleigh (John William Strutt, 3rd Baron Rayleigh). The unit, Rayleigh, is named in honor of #4, commonly known as Robin.

#3 established a laboratory at Terling Place, the family’s residence. #4 resigned his chair in physics at Imperial College after #3 died in 1919 and continued his research in the laboratory at Terling Place. Gentleman (or independent or citizen) scientists understand the benefits of WFH (working from home).

Unlike electronics, vintage optical datasheets are harder to find online. Here are some comments uncovered from a confidential US document that looked at materials and methods from 1920-1950 (G.L. Harvey, “A Survey of Ultraviolet Communication Systems,” NRL Report 6037, March 13, 1964):

“Corex D is useful for bulbs on sunlamps as it transmits the erythema or sun tanning wavelengths which are most effective at about 2967A while cutting out the less desirable germicidal mercury line at 2537A. The most effective wavelength for germicidal effectiveness is 2600A, dropping to very little bactericidal action at 3200A.”

Corex D appears to be Corning 970. Corex A (red-purple glass) appears to be Corning 986 or 986A (think black-light lamp). Clear Corex A appears to be Corning 980. But, this could be wrong. When material properties or some datasheets are found, they will be posted. It would be nice to see confirmation of #4 Lord Rayleigh’s observations of double refraction in Corex.

Corning Print Ad, 1938

For more information on the optical work of #4, see his son Charles R. Strutt’s article, “The Optics Papers of Robert John Strutt, Fourth Baron Rayleigh,” Applied Optics Vol. 3, No. 10, p. 1116-1119 (October 1964). Charles is the father of #6, John Gerald Strutt, The Lord Rayleigh.