Last Updated: Aug 24, 2018     Views: 87

Image: Workmen Posing before the Disk. Photograph by Ayres A. Stevens, Corning Glass Works, Corning, New York. Rakow Research Library, Bib ID: 117698. New York Heritage Digital Collections, ID: 1000101817.

Hello! Thank you for your question. Dr. George McCauley, who designed and supervised the casting of the 200-inch mirror, explains, "Removing the cores from the ribs of the disk and cleaning its surface is accomplished with a sharp-edged bar and a sandblast and presents no great problem; except, of course, great care must be exercised, if a bar is used, that the glass be not struck too severely. Removing the cores with a bar must be classed more as work than as a problem. The sandblast works slower, with more dust, but easier, and is ideal for cleaning the entire surface that has been in contact with the mold (McCauley, George V. "Some engineering problems encountered in making a 200 inch telescope disk." Bulletin of The American Ceramic Society 14, no. 9, Sept. 1935, 300-322).

Online Resources

There are several resources on The Corning Museum of Glass website and elsewhere online that might be of interest to you:

Research Guide

"The 200" Disk and the Hale Reflecting Telescope," Rakow Research LIbrary, The Corning Museum of Glass.

Selected Print Resources



  • diCicco, Dennis. "The Journey of the 200-Inch Mirror." Sky & Telescope 71, no. 4 (April 1986): 347-348.
  • Learner, Richard. "The Legacy of the 200-Inch." Sky & Telescope 71, no. 4 (April 1986): 349-353.
  • Rhodes, Richard. "Reflected Glory: How They Built Palomar." American Heritage Invention and Technology 1, no.1 (Summer 1985): 12-21.

Borrowing Library Materials

If you wish to borrow copies of library items, please contact your local library. The Rakow Research Library will lend designated books from its collection and will send copies of articles requested by other libraries. Your library can request items through the OCLC WorldShare Interlibrary Loan (ILL) system or by direct request through email at For more information, please see our ILL policies and procedures.

Please let us know if there is anything specific that we could assist you in finding.

A more extensive list of resources is available upon request. Please let us know if we can be of further assistance via Ask a Glass Question (, email (,
phone (607-438-5300), or text (607-821-4029).






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