Answered By: Beth Hylen Last Updated: Sep 30, 2016 Views: 82
So far, I have not been able to find the precise refractive index of an equilateral prism of Steuben glass. I am continuing to contact colleagues who may be able to answer the question.
I attached some basic information about the refractive index of glass. Steuben is a lead glass noted for its brilliance, so you can assume a very high refractive index.
This description from Wikipedia is useful for understanding how prisms (in any type of glass) use light: "Prisms are sometimes used for the internal reflection at the surfaces rather than for dispersion. If light inside the prism hits one of the surfaces at a sufficiently steep angle, total internal reflection occurs and all of the light is reflected. This makes a prism a useful substitute for a mirror in some situations." http://en.wikipedia.org/wiki/Prism_(optics)
In his book, Scenes and Signs on Glass, Laurence Whistler describes his theoretical use of light and glass: [The Cupid Press 1985, p. 13]
"Glass is a good medium for expressing notions of light, because the engraver works exclusively in light, arresting it on the surface -- catching it by scratching -- then using it as paint or as ink, being incapable of adding one shadow to the picture, leaving shadow to pretend to be there when really it is only the dark background (always granted a dark background), as it shows through the places unengraved. Viewed against a uniform pale sky the picture becomes muted or as if erased. The light needs the dark to be articulate. Which may be true of life itself, and the meaning of the darkness in it, granted one is open to a meaning. Positive and negative are in perpetual necessary balance; but he positive is light, and only light.
"This paradox and this elusiveness are in the nature of clear glass, considered as a minor graphic medium. The engraved image hangs insubstantial and precarious, uncertainly suspended, as it seems, on nothing."
His son, Simon Whistler, provides further clues: "Glass.... It will allow light to pass virtually unhindered through it, but can appear also to contain light in its structure. Ambiguous and illusory it lends itself to ideas that explore these characteristics. My own analogy of glass is to imagine that it is actually made of light: light trapped between two polished skins. Scratch the surface and light is released at that place. The engraver's task is to find and release the light in the way that best expresses his ideas...." Whistler, Simon. On a Glass Lightly. Libanus Press, 2004; 2nd ed 2006, pp. 19-20. "The source of light should be behind the engraving and shine towards the viewer, with the background dark or shadowy. Badly lit engraving looks dead, if not actually invisible...." pp. 20-21.
I attached a bibliography for Whistler and his family, including a book about the piece you mentioned (it does not reveal the secrets of his work on the prism):
Booker, Christopher. Laurence Whistler: the glass engravings in Salisbury Cathedral. Christopher Booker and Ian Dunlop. Salisbury, [England]: Salisbury Cathedral, 1990. 16 p.
I hope this information is helpful. I will continue to look for a better explanation of the optics involved in Whistler's Salisbury Cathedral prism piece.
Thank you very much for your reply. I have looked at your response in detail and am extremely grateful for all the trouble you have taken to provide such a comprehensive reply.
I am familiar with many of the references in the bibliography, but some were completely new to me; two are of particular interest, namely :
Memorial window to Edmund Blunden, 1896-1974 : in the Church of St. Peter & St. Paul, Yalding, Kent
[S.l.: s.n., between 1979-1995].  leaves.
Window engraved in 1979 by Laurence Whistler, a friend of the poet.
Location : Stacks
Call Number : NK5198.W5 M53
Location : Microforms
Call Number : F-15022
Homage to Jacqueline du Pre
The Guild of Glass Engravers Newsletter
Summer 1996, pp 6-7
Engraved panel by Laurence and Simon Whistler in the new Music Theatre, Oxford
Please could you tell me whether you operate a research service for those who are unable to visit the Rakow Research Library in person and, if so, how much it would cost for me to obtain a copy (electronic or otherwise) of each of the above for my own private use?
Thank you once again for all your help; I look forward to hearing from you.
In a separate email message I am sending scans of the items you requested.
We do not have a research service at the Rakow Library, however, we participate in Interlibrary Loan:
"If you wish to obtain copies of library items, please contact your local library. The Rakow Research Library is a member of the Online Computer Library Center (OCLC). Your library can contact us through OCLC or they may send an Interlibrary Loan form to us by e-mail. We send copies of articles and will also loan certain books if a second copy is available in the library collection. Books are loaned for a four week period. For further information, please see our web page: http://www.cmog.org/research/library/about/interlibrary-loan."
Please let me know if you have further questions.