Answered By: Regan Brumagen
Last Updated: Dec 10, 2016     Views: 118

Thank you for your inquiry. We are working on your questions. Below I have provided you with some information on the Palomar mirror and also would like to clarify your question about our Museum object. I am attaching bibliographies on obsidian and mirrors so that you can browse through them and let me know if anything sounds of particular interest. Should you like to view the books, you can do so in our library hours 9-5 Monday - Sunday. You can take the lists to your local library and if they do not have a specific title, they will be able to request it through Inter-library Loan for you.

My colleague, who had written the text for the Palomar exhibit that we had in the library (, has sent this response to your question: "George Ellery Hale was the force behind the building of Palomar Observertory. Hale built the 60 inch reflecting telescope and than a 100 inch telescope which was installed at the Hooker Observatory, but he was convinced it was possible to build a 200 inch telescope. First, however, Hale had to find a company capable of creating such a large piece of glass. He began by commissioning the General Electric Company to make a disk from fused quartz. This effort failed to meet his requirements, however, and Hale began to look elsewhere. Corning Glass Works convinced Hale that its Pyrex glass could be used to produce a telescope mirror of the size that he desired. Pyrex was a strong glass with few imperfections. Hale decided to award the commission to Corning, and Dr. George V. McCauley, a physicist at that firm, was assigned the task of determining how such a disk could be made. McCauley began to make increasingly larger disks, using a process he had devised for casting huge pieces of glass. He created 26-, 30-, 60-, and 120-inch disks before finally preparing to produce the 200-inch disk. In 1934, two 200-inch disks were cast by Corning Glass Works under McCauley’s direction. The mold for the 200-inch disk was constructed in a manner identical to that employed for the 120-inch disk cast by Corning Glass Works in 1933. The 200-inch mold had 114 tall cores cemented to the bottom. Twenty-two of these cores broke loose during the first pouring, ruining the honeycomb design necessary to create a disk strong and yet light enough to be workable. Three ladles were used in the pouring of the 200-inch disk. As one ladle of glass was emptied into the mold, another was filled and trolleyed from the melting furnace to the mold. Each ladle held about 750 pounds of glass, although only a third of that glass made it into the mold during each pour. The rest was reintroduced into the furnace to be remelted. The crew poured about 100 ladles of glass during the operation. After the first disk failed, McCauley asked executives at Corning Glass Works if he could make another 200 inch disk. They agreed, and McCauley set out to improve the process and to produce a better disk. The second disk, a successful casting, was transported to California, where it was ground and polished over an 11-year span. Work on the disk had to be suspended during World War II, but after the war the disk was completed and installed in the Hale Telescope at Palomar Observatory. The first disk remained in Corning, where it was displayed in Pine Street Square (now known as Centerway) in its own custom-built museum. In 1951, the disk was moved to the site on which a new museum of glass and glass center were being constructed, across the Chemung River from downtown Corning. It was installed in the Corning Glass Center, where it was the first sight for visitors entering the complex. In 1999, the disk traveled again to the Glass Innovation Center in The Corning Museum of Glass where it remains."

For more information, we have bibliographies on Palomar we can send or you can look for these books at your local library:

. Watson, Fred. Stargazer: the life and times of the Telescope. Cambridge, MA: Da Capo Press, 2004. p. 264

2. Florence, Ronald. The Perfect Machine: Building the Palomar Telescope. New York: HarperCollins, 1994. p. 198. I hope you find this information helpful.

Please let me know about your museum object question and if there are any particular obsidian / mirror sources that seem like they would be a good fit for your research, or if you have trouble opening any of the attachments. Attachment(s) included: Mirrors early .doc, Mirrors making.doc, Obsidian.doc, Natural glasses - obsidian.doc Accession Number 62.7.2 A (listed as not on display) Accession Number 70.7.1 Regarding piece 70.7.1: Here is an excerpt from a note that accompanied the piece: "Obsidian mirrors of various sizes and shapes are known from all over Middle America and some of them date back at least to the Classic period; however, they are most commonly larger in size and, in general, fancier in the Postclassic, and particularly in the Aztec culture. Friedman's hydration measurement on the mirror in question, which places it at about 1400 to 1500 A.D. is, of course, just right and it is likely that this is an Aztec specimen. I know of no monograph or article devoted to these mirrors, although a more careful review of the literature, might turn up something. Such mirrors are frequently illustrated. For example, in Keleman's "Medieval American Art," Volume 2, Pl. 298a, there is a splendid example of a circular mirror contained within a carved wooden frame. This particular piece is believed to come from Vera Cruz and I would guess that it is contemporaneous with Aztec. Such mirrors are also referred to in general books, for instance, Vaillant's "Aztecs of Mexico," the 1962 edition, see p. 116."  We don't seem to have much more on that 2nd piece. This article on our website would likely be helpful: 

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