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John Clyde Hostetter Collection on the 200" Disk

Identifier: MS-0072

Scope and Contents

The bulk of this collection consists of approximately 185 photographs, documenting Corning Glass Works’ creation of the 200” glass disk, which became the mirror of the Hale telescope. Although Hostetter collected these photographs, they were taken by others, including Ayres A. Stevens of Corning, NY. Some duplicate or are similar to photographs in the George V. McCauley Papers. The collection also includes a small amount of personal and glass-related miscellany from Hostetter.


  • 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, director of Research and Development at Corning Glass Works during the creation of the 200” disk, was born on February 18, 1886, in Williamsport, PA. He studied chemical engineering at Bucknell University, where he received a BS in 1908 and an MS in 1909. He married Ida May Fischer, and the couple had a son, whom they named John Robert.

Before coming to Corning Glass Works, Hostetter worked as a chemistry instructor at Bucknell University (1908-10), as a chemist at the US Standards Bureau (1910-12), and as a physical chemist at the Geophysical Lab of the Carnegie Institute (1912-19). In 1919, he joined the Corning Glass Works as manager of the Steuben Division. He served in a variety of other positions at Corning as well, including assistant to the vice president (1922-24), manager of the company’s Rhode Island division (1924-28), and manager of its 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 of Welsh Refractories Corporation from 1944 to 1950. In 1950, he retired to Winter Park, Florida, having received a variety of 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 until the 1990s, the world’s largest functioning telescope was the Hale telescope, located on Mt. Palomar in California. The mirror for the telescope, 200” in diameter, was cast in 1934 by the Corning Glass Works in Corning, NY, and 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 when noted astronomer George Ellery Hale asked the International Education Board, one of the philanthropies funded by the Rockefeller family, to support the design and construction of a 200” telescope, to be located near Pasadena, California, on Mt. Palomar. By the completion of the telescope, the project cost $6,550,000, and had been funded by two additional Rockefeller philanthropies: the General Education Board and the Rockefeller Foundation.

In 1931, Corning Glass Works was asked to create a borosilicate glass blank for the telescope’s mirror. Corning 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.

Because of the massive quantities of glass involved—75,000 pounds of glass were melted, and 42,000 pounds were actually poured into the mold—and the high temperatures—the temperature in the melting furnace when the glass was poured was 2800º—the team designed special equipment to perform these procedures. 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, and arrived at the Mt. Palomar Observatory’s optical shop at CalTech on April 10. At the optical shop, the disk was ground to its final shape. Because of the heat and energy generated by the grinding process, only a small amount of grinding could be performed at once. Before grinding began, it was estimated that this would take up to three years. However, work was interrupted by World War II, and was not completed 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.


2.6 Linear Feet


The collection is arranged in two series: Series I. Photographs, 1934-1936; and Series II. Personal and Glass-related Miscellany, 1939-1943.

Custodial History

Acquired 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
Rebecca Hatcher
July 2002
Description rules

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