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John Clyde Hostetter Collection on the 200" Disk

Identifier: MS-0072

Scope and Contents

The collection is mainly photographs documenting the creation of the 200” glass disk, made by Corning Glass Works of Corning, New York. Although Hostetter collected these photographs, they were taken by others, including Ayres A. Stevens of Corning, New York. Some images appear to be duplicates or visually similar to those found in the George V. McCauley Papers. Contents also include personal and other glass-related materials from Hostetter.

This collection consists of two series:

(1) Photographic Materials, 1934-1936

(2) Miscellaneous and Personal Materials, 1939-1943


  • 1934-1943


Conditions Governing Access

This collection is open for public research. Researchers must make an appointment to view this collection.

Conditions Governing Use

The Copyright law of the United States (Title 17, United States Code) governs the making of photocopies or other reproductions of copyrighted material. Under certain conditions specified in the law, libraries and archives are authorized to furnish a photocopy or other reproduction. One of these specified conditions is that the reproduction is not to be "used for any purpose other than private study, scholarship, or research." If a user makes a request for, or later uses, a photocopy or reproduction for purposes in excess of "fair use," that user may be liable for copyright infringement. The user agrees to defend, indemnify, and hold harmless the Corning Museum of Glass and the Rakow Research Library against all claims, demands, costs and expenses incurred by copyright infringement or any other legal or regulatory cause of action arising from the use of Library materials.

Biographical / Historical

Dr. John Cylde Hostetter was born on February 18, 1886, in Williamsport, Pennsylvania. He studied chemical engineering at Bucknell University, where he received a B.S. in 1908, and an M.S. in 1909. He married Ida May Fischer, and together had a son, John Robert.

In his early career, Hostetter worked as a chemistry instructor at Bucknell University (1908-10), as a chemist at the U.S. Standards Bureau (1910-12), and as a physical chemist at the Geophysical Lab of the Carnegie Institute (1912-19). In 1919, he joined CGW as manager of the Steuben division. He also held a variety of other positions, including assistant to the vice president (1922-24), manager of the company’s Rhode Island division (1924-28), and manager of the bulb and tubing department (1928-30). In 1930, he became director of research and development, a post he filled until 1937. From 1931 to 1936, he directed the task of casting the 200” disk.

After leaving Corning in 1937, Hostetter became vice president and director of research at Hartford-Empire Co., where he remained until 1944. From 1944 to 1949, he served as president of the Mississippi Glass Co., and was on the board of directors at Welsh Refractories Corporation from 1944 to 1950. In 1950, he retired to Winter Park, Florida, having received multiple awards for his contributions to science during his career. He died on April 2, 1962.


“The Glass Giant of Palomar.” Bucknell Alumnus, July 1968: 10.

Biographical / Historical

From the 1940s to the 1990s, the world’s once largest functioning telescope was the Hale telescope, located at the Palomar Observatory in California. The mirror for the telescope, 200” in diameter, was cast in 1934 by Corning Glass Works (CGW) in Corning, New York. It was then transported across the country to California in 1936. There, the disk was ground to its final shape, coated with a thin layer of aluminum, installed in the new telescope, and dedicated on June 3, 1948.

Development of the Hale telescope began in 1928. Noted astronomer, George Ellery Hale, asked the International Education Board (Rockefeller Foundation) to support the design and construction of a 200” telescope, to be located on Mt. Palomar near Pasadena, California. Upon completion of the telescope, the project cost $6,550,000, which was primarily funded by the Rockefeller Foundation.

In 1931, Corning Glass Works (CGW) was asked to create a borosilicate glass blank for the telescope’s mirror. CGW accepted the challenge, and a team of researchers led by Dr. George McCauley began developing equipment and procedures, which they hoped would allow them to cast the blank successfully. They planned to heat the necessary glass in a melting furnace, ladle it into a mold, which was enclosed in a pouring oven to keep the glass hot and fluid, then carefully cool the glass. Cooling would begin in the pouring oven, then the glass-filled mold would be lowered, moved, and raised into an annealing kiln, where it would finish cooling.

75,000 pounds of glass were melted, of which 42,000 pounds were poured into the mold. Such vast quantity of glass required furnace temperatures of 2800° F, and would prompt the team to design special equipment to continue production. To test their equipment and procedures, workers cast several smaller mirror blanks, with diameters ranging from 30” to 120”. These small blanks were also ground to shape and coated with aluminum to serve as auxiliary mirrors in the finished telescope.

In spite of these tests, a problem occurred when the team first poured molten glass into the 200” mold. In order to reduce the amount of glass in the disk, and reduce the disk’s weight to more manageable 20 tons, the mold included a series of cores, arranged to produce hollows in the back of the blank without weakening the disk. These cores were attached to the mold with metal rods. On March 25, 1934, during the first pour, the rods melted and the cores floated up into the glass. Efforts to remove the cores left the surface of the disk pitted, and an attempt was made to reheat the disk in the annealing oven in order to repair these flaws. Although this did improve the surface, the annealing oven was not designed to melt glass, but to control the cooling of glass. As a result, the roof collapsed on the disk and left an impression on the glass. It was decided to begin a second disk, but also complete the flawed disk, in order to test the annealing process. This flawed disk now stands in the Corning Museum of Glass.

The second disk, which became the mirror in the Hale telescope, was cast successfully on December 2, 1934. Over the course of the next year, the glass was cooled to room temperature at a rate of between one and two degrees Fahrenheit per day. When the disk reached room temperature, workers lowered it out of the annealer, removed the mold and cores, and checked the glass for strain. When it had passed inspection, the disk was loaded onto a custom railroad car and transported to California. The train left Corning on March 26, 1936, arriving at the optical shop of Palomar Observatory at the California Institute of Technology (CalTech), on April 10. While there, the disk was ground to its final shape. Due to high heat and energy generated by the grinding process, only a small amount of grinding could be performed at one time. Grinding was estimated to take up to three years, however, work was interrupted by World War II, and was not finished until October 3, 1947.

The grinding process removed about 5.25 tons of glass, and created a section of a sphere, accurate to 2 millionths of an inch. The disk was then coated with aluminum to form a mirror, installed in the telescope, and dedicated on June 3, 1948, when it was named for George Hale, who had died in 1938.


Corning Glass Works. The Mirror of Mt. Palomar. Corning, NY: Corning Glass Works, 1953.

John Hostetter. “Pouring the 200” Disk,” from the Document Collection of the Rakow Research Library.


2.5 Linear Feet (2 Flat Boxes)

Language of Materials


Immediate Source of Acquisition

Received from the heirs of Dr. John Clyde Hostetter in 2001.

Related Materials

George V. McCauley Papers
John Clyde Hostetter Collection on the 200" Disk, 1934-1943
A Guide to the Collection
Under Revision
Rebecca Hatcher
July 2002
Description rules
Describing Archives: A Content Standard
Language of description
Script of description
Edition statement
Revised by Amanda LaLomia in 2019: Structure and format reconfigured to improve clarity and thoroughness. Needless series and sub-series were eliminated as needed. Fields previously left blank were filled accordingly.

Repository Details

Part of the The Rakow Research Library Manuscript Collection Repository

The Rakow Research Library
The Corning Museum of Glass
Five Museum Way
Corning NY 14830 USA