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From Wikipedia, the free encyclopedia

Photosensitive glass is a crystal clear glass in which microscopic metallic particles can be formed into a picture or image by exposure to short wave radiations such as ultraviolet light.[1][2][3]

Contents

Exposure process

When the glass is heated to very high temperatures for several hours the latent image is converted to a visible image through photoexcitation.[1][3] Exposure through photographic negatives permits the development of three dimensional color images and photographs.[1][3]

Photosensitive glass is used in printing and reproducing processes.[4] Photosensitive glass is like traditional camera film except that it reacts to ultraviolet (UV) light, where camera film responds to visible light.[3][5] The ideal wavelength to use for exposure should be between 300-350 nm, with 320 nm being optimum.[4]

Photosensitive glass contains microscopic metallic particles.[5] These microscopic metallic ion nanoparticles are made of gold or silver which is responsible for the refractive index change.[5] Photosensitive glass is similar to photographic film. Photographic film uses chemicals, while photosensitive glass uses gold or silver ions in the material that will respond to the action of light. [4] The process is to pass light of the ultraviolet wavelength through a negative on the glass.[5] Photographic resolution can be obtained with adhesive polyester as a reverse negative, however anything which resists UV light can act as a "negative."[4]

The glass is sensitive to light that can be ultimately turned into a permanent picture with a heat process "fixing" permanently the image.[3][4][5] Silver glass "latent images" will develop in 3-4 hours at 886°F - 976°F. [4] Gold glass "latent images" require a higher temperature of 968°F - 1058°F and over a similar period of time for postbaking. [4] Postbaking hastens the occurrence of the particles with the shadow areas of the negative, permitting deeper penetration into the glass than the highlighted areas.[4][5] This gives the picture three dimensions and color.[4][5]

The photograph is developed by heating the photosensitive glass around 1000°F for several hours after exposure.[5] The glass itself is photosensitive and produces a three dimensional image.[1] Particles that are invisible to the naked eye (i.e. gold or silver) are in the glass. These microscopic particles move and grow when heated to form the photographic image itself.[1] The process is similar to camera film, however a "negative" is placed on top of the photosensitive glass and then exposed to ‘’’ultraviolet’’’ light. Camera film, of course, would be exposed to ordinary visible light. Then there is a special process for the exposed photosensitive glass. The glass is reheated then in a kiln and postbaked for several hours. The image then "appears" within the special exposed glass as if by magic. The heated piece of photosensitive glass is then allowed to cool down and the process is done. The positive images produced within photosensitive glass comes in a variety of colors.

As a material for the hot glass studio artist, an additional method of producing imagery in an object using photosensitive glass is to first blow an extremely thin rondel (cased or otherwise) which is annealed in the typical manner. That rondel is then cut into sections which are exposed under a negative. Next, those sections (containing the latent image) are warmed and applied to the surface of a gather of hot glass on the blowpipe. As the object is completed over several furnace reheats, the heat develops the image as the object is being created. This method specifically eliminates the need for the reheating of the object in a kiln for development, which consumes considerable oven time, energy, and the risk of loss or damage due to shattering on the way up to temperature, or more importantly, slumping while being held at temperature. The timing of the glassblower determines the final degree of development, and simple choices of form minimize distortion in the image.

Since the image is inside and actually a part of the glass itself, photosensitive glass is the most durable photographic medium known.[1][5] It is claimed that a photo image within photosensitive glass is the most durable form of photography and will last as long as the glass itself.[1][2][5] The photographic image is ‘’’not’’’ on the surface of the glass, but internally.[1]

Fluorescent photosensitive glass makes it possible to make fluorescent photographs and fluorescence holography.[6]

Photosensitive glass is different than photochromatic glass.[3] Photochromatic glass is used in self-darkening sunglasses which darkens when exposed to bright daylight.[3] It then returns to see-through transparency when strong daylight is removed and can then be used indoors as regular glasses.[3]

History

Photosensitive glass was invented in November 1937 by Dr. Donald Stookey of the Corning Glass Works.[1][2] It was not announced publicly until ten years later on June 1, 1947.[1][2] It was officially patented in 1950 by Stookey as U.S. Pat. No. 2,515,937 and U.S. Pat. Nos. 2,515,943 with gold microscopic particles.[1]

Little has been done to develop the product since its patent.[1] It is labor intensive and has a high cost. [1] Only large commercial glass factories produce it.[1] In the 1980’s photosensitive glass was created to a small degree to be used in "hot glass" work.[1] Then individual artists owned smaller studios and created works in blown glass and began experimenting with photosensitive glass.[1] Going into the Twenty-First Century only a few glass artists know the technique of achieving good results with photosensitive glass.[1]

Military applications

One of the reasons between the time photosensitive glass was invented and the delay why it was announced approximately ten years later to the public is because of its military applications.[4] It is possible to burn images and words that are hidden in photosensitive glass until heated at a high temperature.[1] The military used this fact during World War II to send secret messages to allied troops in pieces of what looked like "ordinary glass."[1] At the other hand, the person who received the "ordinary glass" just had to heat it up to read the hidden message.[1] Because of this application photosensitive glass was kept secret until the end of World War II.[1][5]

Building applications

The United Nations Building is faced with hundreds of square feet of photosensitive glass.[7]

References

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Bibliography

  • Encyclopaedia Britannica, The New Encyclopaedia Britannica, v.8 Macropaedia Ge-Hu, Encyclopaedia Britannica, 1974, ISBN 0-8522929-0-2
  • Parker, Sybil P., Dictionary of Scientific and Technical Terms. McGraw-Hill Companies, Inc., (2003) - "photosensitive glass," ISBN 0-0704231-3-X,
  • Maluf, Nadim et al., Introduction to Microelectromechanical Systems Engineering, Artech House, 2004, ISBN 1-5805359-0-9
  • Paul, Amal, Chemistry of Glasses, Springer, 1990, ISBN 0-4122782-0-0
  • Stookey, S. Donald, Journey to the Center of the Crystal Ball : An Autobiography, American Ceramic Society (1985), ISBN 0-9160946-9-3
  • Stookey, S. Donald, Explorations in Glass: An Autobiography, Wiley-Blackwell (2000), ISBN 1-5749812-4-2

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