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Send Orders for Reprints to [email protected] Recent Innovations in Chemical Engineering, 2014, 7, 000-000 1 A Short History of Photosensitive Glass Patents Marcio Luis Ferreira Nascimento1,2* 1Vitreous Materials Lab, Institute of Humanities, Arts and Sciences, Federal University of Bahia, Rua Barão de Jeremoabo s/n, Idioms Center Pavilion (PAF IV), Ondina University Campus, 40170-115 Salvador, Bahia, Brazil; 2PROTEC/PEI — Postgraduate Program in Industrial Engineering, Depart- ment of Chemical Engineering, Polytechnic School, Federal University of Bahia, Rua Aristides Novis 2, Federação, 40210-630 Salvador, Bahia, Brazil Received: January 00, 2015 Revised: March 00, 2015 Accepted: March 00, 2015 Abstract: The development of photosensitive glass (PG) has a remarkable history since its first com- mercial discovery in the 1940s. The manufacturing of PG is one of the most widely reported methods M.L.F. Nascimento for special glass manufacturing. PGs are capable of forming permanent photographic images when subjected to light, pro- viding security, high quality and productivity. The first U. S. patent about photosensitive glass was filed on December 8th, 1943, and published July 18th, 1950, by Stanley Donald Stookey. A historical perspective about photosensitive glass rep- resents an important step for future applications. PG has been considered one of the most interesting research areas with potential industrial applications. A number of companies and institutions have explored the usefulness of such special glasses. In this paper, we investigated the number of published manuscripts and patents and determined the correlation of research activities to the production of new PG materials. The United States, Japan and China have been leaders in photosensitive glass development and have contributed to an impressive rise of activity in PG based on a number of new publications, author keywords, affiliations and primary characterization techniques. We verified that the number of published fundamental PG studies was greater from academic institutions than from industrial laboratories. According to the Euro- pean Patent Office, more than 6,228 patents have been globally filed prior to 2013 with the terms “photosensitive” and “glass” within the title or abstract. These numbers have continued to grow along with worldwide PG-related sales. Based on the Scopus database, for the same period, 1,301 PG documents (primarily manuscripts) were published with the same terms in the title, abstract or keyword list. Statistically, there have been fewer worldwide publications of manuscripts than patents. Keywords: Glass, history, photosensitive, patent, technology. 1. INTRODUCTION on a clear glass and briefly exposed to ultraviolet radiation from any of the several sources, including sunlight, sunlamps One decade after the first patents and manuscripts were or other similar sources. After the negative is removed, the published in the 1940s, a new type of commercially innova- figure (or photograph) is fixed by increasing the temperature tive material was introduced: the photosensitive glass (PG) of the glass to approximately 600°C for a few minutes [1, 2]. [1]. It was discovered by the chemist and inventor Stanley The novelty of the procedure is in the mixing of transparent Donald Stookey at Corning. PGs are in the field of material metallic nanocrystals (e.g., gold, silver or copper) in trace sciences and engineering and are based on the kinetics and quantities. On additional heat treatments, these nanocrystals crystallization mechanisms of vitreous materials, which are act as crystallization seeds or nuclei for the growth of non- essential for the development of such special glasses. These metallic crystals. Thus, the phenomena of crystallization materials have a number of special properties. PGs were occurs, confining an image or figure [1, 2]. Filed by Robert originally categorized as a new photographic medium that H. Dalton, a colleague of Stookey at Corning, in 1943 (stud- made possible the permanent printing of 3D colored images ies started in 1937 [4]), the first patent considered the use of within crystal-clear glasses [2]. According to Stookey, “photo- copper as a nucleating agent [5]. However, the term “photosensitive glass” [3] refers to “certain silicate glasses containing sensitive” was not used in this patent, and it was not feasible atomic species that are able of forming stable photographic to produce images or display kinetics, as was later done by images or figures into clear glass when subjected to light”. Stookey [3, 4]. In fact, Stookey’s patent was not published In fact, to reproduce a figure, a negative is positioned until almost seven years later on July 8th, 1950 [6]. Two patents were awarded to Stookey: U.S. Pat. Nos. 2,515,937 *Address correspondence to this author at the Vitreous Materials Lab, and 2,515,943; the first is shown in (Fig. 1). Institute of Humanities, Arts and Sciences, Federal University of Bahia, Rua Photosensitive glasses and glass-ceramics have some Barão de Jeremoabo s/n, Idioms Center Pavilion (PAF IV), Ondina Univer- sity Campus, 40170-115 Salvador, Bahia, Brazil; Tel: +5571 32839803; characteristics in common: they are transparent, strong and Fax: +557132839801; E-mail: [email protected] tough, chemically durable, and have zero or low porosity. Websites: www.lamav.ufba.br; www.protec.ufba.br These materials have been used in a wide array of applications, 2405-5204/14 $58.00+.00 © 2014 Bentham Science Publishers 2 Recent Innovations in Chemical Engineering, 2014, Vol. 7, No. 2 Marcio Luis Ferreira Nascimento Fig. (1). Left: the first page of United States photosensitive glass patent U.S. 2,515,937 applied on December 8th, 1943, [6] and published on July 8th, 1950. Right: an image application of the photosensitive process; there is a bluish portrait of the author as the first figure in the patent. At that time he used gold particles with a basic glass, with heat treatments between 500 to 600°C over a few minutes. See www.uspto.gov. ranging from portraits and figures, photographic murals, 3D Initially, the manufacture of glass-ceramics was empiri- images, decorative windows, displays, ornamental tiles, and cal and based on experimentation. The history of glass- many engineering applications, including military uses. ceramic production dates back a century to 1898 when Gus- tav Tammann [8] published the first modern scientific paper Glassmaking is an old technology that dates back ap- on glassmaking, which described the behavior of glass- proximately 5 millennia. Glass is one of the most relevant, ceramics production by controlling the nucleation I and useful and effective materials throughout human history. The process of glassmaking consists of melting raw materials, growth U processes. He studied the crystallization of organic liquids and suggested the following method, which is now such as sand, alkali carbonates and lime, at approximately known as the Tammann, or “development” approach [9]. 1400°C. This has been a common technique throughout Crystals nucleated in a glass matrix at a low temperature, T , recorded history due to its simplicity, adaptability and poten- n are developed to sizes sufficient for microscopic observa- tial applications in a number of fields. Glassmaking can also tions at a higher temperature, T > T . The development be modified for mass production. As noted by Zanotto [7], d n the thermodynamics and kinetics of nucleation and crystal temperature Td is determined based on rules for the nucleation (I) and growth (U) rates: the nucleation rate at T [I(T )] growth are key scientific problems that control the glass- d d should be lower than the nucleation rate at T [I(T )], and the forming ability of molten liquids and the terminal stability of n n growth rate at T [U(T )] should be greater than the growth glass against devitrification. The basics behind the nature d d rate at T [U(T )]. In the last half century, this process has and rules of glass crystallization involve the mechanisms, n n gained widespread popularity in academia as a method for thermodynamics and kinetics of crystal nucleation, growth and overall surface crystallization. the manufacture of homogeneous glassy materials. Stookey A Short History of Photosensitive Glass Patents Recent Innovations in Chemical Engineering, 2014, Vol. 7, No. 2 3 empirically determined the characteristic temperature Td of launched glass-ceramics [12,13]. Stookey once said, “I am photosensitive glasses. most proud of opening up a whole new field of science – the nucleation of crystallization of glass – that produced all types Recently, Glebov [10] proposed a kinetics model of a of new crystalline products with so many different useful photoinduced process based on a new photosensitive composition for 3D hologram production, photo-thermo-refractive properties.” [11]. In 1987, Stookey retired from Corning Glass Works. glass (PTRG). PTRG is a multicomponent silicate glass composition with cerium, silver and fluorine as the primary Our objective is to present an overview of the historical dopants, which shows a decreasing refractive index after tendencies and current status of PG studies. We hope this exposure to UV light and thermal heat treatment. In this paper can be used during discussions about future guidelines material, a sequence of photochemical and photo-physical for photosensitive glass studies by describing the develop- reactions occurs as follows: i) a UV incident light photoion- ment of PGs based on the literature.

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