JAIC 2005, Volume 44, Number 2, Article 3 (pp. 95 to 102)
JAIC online
Journal of the American Institute for Conservation
JAIC 2005, Volume 44, Number 2, Article 3 (pp. 95 to 102)



ABSTRACT—Most collections of ethnographic, historical, and artistic artifacts of the 19th and 20th centuries include a considerable selection of semi-synthetic molded plastics. Often conservators have difficulty identifying them and determining their origins and dates. Patents can help, especially when the material composition of an object is unknown but there is information on its date of manufacture, or when the nature of the material is known but not when the object was made. Some objects bear a patent mark on their surface. A study may elicit information as to the date of the patent, the inventor, and in some cases even the material of which it is made. The patent provides extremely useful information on chemical composition, from which the chemical and mechanical properties of artifacts can be determined, and hence requirements for their proper preservation and conservation.

TITRE—Les brevets d'invention en tant qu'aide lors d'études sur l'histoire et la composition des plastiques semi-synthétiques. RÉSUMÉ—La plupart des collections d'objets ethnographiques, historiques et artis-tiques des 19ème et 20ème siècles incluent un nombre considérable de plastiques semi-synthétiques produits par moulage. Souvent les restaurateurs ont des diffi-cultés à les identifier et à déterminer la date et l'en-droit où ils ont été fabriqués. Les brevets d'invention peuvent aider à ces recherches, surtout quand la composition d'un objet est inconnue mais qu'il existe des renseignements sur sa date de fabrication, ou quand la composition est connue mais pas la date de fabrication. Certains objets portent une marque de brevet sur leur surface. Une étude peut fournir des renseignements quant à la date du brevet, l'inventeur et dans certains cas même les matériaux dont l'objet est composé. Un brevet d'invention fournit des renseignements extrêmement utiles sur la composition chimique, à partir de laquelle les propriétés chimiques et mécaniques des objets peuvent être déterminées et suivant cela, les conditions nécessaires pour leur préservation et les traitements de conservation.

TITULO—Las antiguas patentes como ayuda para el estudio de la historia y composición de los plásticos semisintéticos. RESUMEN—La mayoría de colec-ciones etnográficas, históricas y artísticas que contienen piezas de los siglos XIX y XX incluyen una gran cantidad de plásticos de moldeo semisintéti-cos. Para los conservadores, uno de los principales problemas que presentan este tipo de objetos reside en la dificultad para datarlos e identificarlos.Las fechas de patente y comercialización de los plásticos pueden servir de ayuda para la correcta cata-logación de la pieza. Salvando algunas excepciones, esta información puede resultar útil en dos sentidos: si se desconoce la composición material de la pieza, pero se dispone de datos sobre su fecha de manufac-tura, se puede descartar cualquier material que no estuviera disponible en dicha fecha. Por otro lado, si lo que se conoce es la composición del objeto, y no su fecha de manufactura, podremos conocer la fecha aproximada antes de la cual ese objeto no pudo haberse manufacturado.Algunos objetos presentan una marca de patente. El estudio de la misma puede proporcionar informa-ción como la fecha de patente, el inventor e incluso, en algunos casos, el material con el que fue fabricado. Las patentes proporcionan una información de gran relevancia sobre la naturaleza y dosificación de los componentes, a partir de la cual se pueden determi-nar su naturaleza físico-química y, por tanto, las estrategias adecuadas para su conservación y restau-ración.

TÍTULO—Patentes Originais Como Uma Ajuda ao Estudo da História e Composição de Plásticos Semi-Sintéticos. RESUMO—A maiorida das coleções etnográficas, históricas e de artefatos artísticos do século 19 e 20 inclui uma seleção considerável de plásticos semi-sintéticos moldados. Frequentemente conservadores têm dificuldade em indentificá-los e determinar sua origem e data. Patentes podem ajudar, especialmente quando o material de composição de um objeto é desconhecido, mas existe informação sobre a data de manufatura, ou quando a natureza do material é conhecida, mas não se sabe quando o objeto foi feito. Alguns objetos trazem a marca patente na superfície. Um estudo pode elucidar infor-mação sobre a data da patente, o inventor e, em alguns casos, até o material do qual o objeto é feito. A patente proporciona informação extremamente útil sobre a composição química, da qual se pode deter-minar as propriedades químicas e mecânicas dos artefatos e, consequentemente, os requisitos adequa-dos para a preservação e conservação.


A patent registers the right of ownership of an invention or technological improvement, protecting the inventor and guaranteeing his or her exclusive right in respect to its manufacture, use, and sale. A patent is frequently claimed not by the inventor but by a company or a representative. Such rights in an invention can also be bought or sold, in which case it will not be the inventor who undertakes industrial production of the product or material concerned.

To apply for a patent, the following details must be given: state of the art, nature of the technical problems that this invention solves, and detailed description of the invention and how it works, accompanied by illustrations if necessary.

The first patents for semisynthetic materials were registered in the United States and Great Britain in the 19th century, by the actual inventors. Synthetic materials, on the other hand, belong to the age of plastics, in which research is undertaken by large companies (e.g., ICI and Du Pont) that then claim and register patent rights.

The rights conferred by registration of a patent are always restricted territorially, and so when the first semisynthetic molding plastics were developed, a patent for a given plastic registered in the United States conferred no rights whatsoever concerning production of the same material in Great Britain. This situation prompted a race to patent any new plastic material in all countries.

The date of the patent for a material or artifact indicates the date when it was registered; this is not generally the date of first industrial production, which would normally take place some years later. However, there are exceptional cases of objects manufactured prior to the patent date. For instance, polymers were developed and used for military purposes years before they were patented and commercialized. Indeed, patents relating to materials and artifacts developed for military purposes have had their publication delayed or have not been published at all, as happened particularly in the years between the two world wars (Van Dulken 1999). Another exception is vulcanized rubber, which was manufactured by Goodyear before the date of the patent. As the industrial importance of such substances increased over time, however, inventors became aware of the need to patent them before commencing production. Despite these exceptions, the patent date helps to place the object chronologically. Generally, it provides the date before which the material concerned could not have been manufactured (Wohler 1998).

Many materials and objects made with semisyn-thetic plastics were never patented, for a variety of reasons, including failures in the application process, ignorance of the patent system, or lack of financial resources. Between 1852 and 1883, a British patent cost £25 and the renewal fees could be as high as £150, a major financial outlay at that time (Van Dulken 1999).

Many 19th-and 20th-century objects bear an inscription containing the date of the patent, which allows for a preliminary approximation of the date of the object. However, given the possibility of error in the inscription, it is always advisable to check the date by examining the original patent and checking its content. If the inscription had a number only, the data can be determined by checking relevant patent year–number tables supplied by patent offices in every country.

The number of a patent and the probable date of its invention or manufacture may also furnish a key to the nationality of the patent, since numbering varies from country to country depending on the dates. A patent number in the region of 100,001 dated c. 1870 would be from the United States, for example, but if c. 1916, from Great Britain; if c. 1873, from France; and if c. 1898, from Germany.

A study of old patents can be complicated by the difficulty of locating them; one of the chief problems is that they have not always been numbered according to a single system. British patents registered between 1617 and 1852 originally lacked numbering and were not published. Objects from this period therefore do not bear patent numbers, although they may bear inscriptions containing the word “patent” followed by the name of the inventor or applicant. With the modernization of patent law in 1852, the 14,359 patents granted up to that time were numbered consecutively in the format no./year (e.g., no. 1/1617; no. 425/1720). This format was maintained up to number 14,359 (no. 14.359/1852), and those patents were published during the 1850s. In 1852 a new system was introduced in which numbers started back at one every year. At this time patents also began to include certain specifications regarding the description of the invention. New changes were introduced in 1916, when continuous numbering began. This commenced with the number 100,001 and continued sequentially (100,002, 100,003, etc.) through subsequent years. A new sequence commencing with 2,000,001 was introduced in 1979.

The first U.S. patent was issued on July 31, 1790, to Samuel Hopkins of Philadelphia. Between 1790 and 1836, patents were not numbered, but they did show ownership and date. The first numbered patent was granted on July 13, 1836; from then on, the numbering has been continuous and consecutive. Since 1790, the United States has issued more than 6.5 million patents.


Research into old patents can be fairly complicated, although recent advances make it possible to find old patents through the Internet. To locate a patent and purchase copies, it is essential to know the patent number and the year of the document. Since October 1998, a network called esp@cenet (website at ep.espacenet.com/ [accessed July 27, 2005]) has furnished information from the patent offices of some countries; the coverage of this search is different in each country. Esp@cenet lists patents from the European Patent Office (EPO), World Intellectual Property Office (WIPO), Japan, and many other countries. Unfortunately, only a very few pre-1920 British patents are available via the Internet.

Another way of searching for British patents is through the British Library, which requires precise details about the subject of the research. This library holds patent records dating back to 1617. If the search is more complex, a research service is available to researchers (">research@bl.uk [accessed July 27, 2005]). If the patent number and year are known, photocopies of the patent specifications can be procured through the British Library Document Supply Centre (dsc-customer-services@bl.uk [accessed July 27, 2005]) or the Leeds Patent Information Unit (piu@leeds.gov.uk [accessed July 27, 2005).

U.S. patents are available over the Internet through the United States Patent and Trademark Office (USPTO) (website at www.uspto.gov/ [accessed July 27, 2005]), whose database allows access to patents granted from 1790 to the present. Patents from 1790 through 1975 are searchable only by patent number and current U.S. classification and only images of these patents are available. For unnumbered U.S. patents (1790–1836) a search can be run by patent number if an X is put in the number field. Many of these old patents are not yet accessible online. All patents from 1976 onward are available in full text, and there are numerous different search criteria—title, issue date, application date, inventor name, etc.


Patent research can furnish very useful data on a given item; nonetheless, the information patents contain must be checked against other documentary sources such as maker's archives, registry dossiers, and product catalogs. In some cases patents contain erroneous or ambiguous data, which may even have been inserted intentionally to confound competitors.

A number of factors can hinder accurate identification and dating of an object from its patent mark. First, the mark may not contain enough information to allow proper interpretation. Second, the patent it refers to may have never been published.

Moreover, the patent mark may take many forms. For example, no rules have ever been established for British patent marks. There might be the name of the inventor or the company followed by the patent number, or the letters BP (British Patent) or PAT (Patent) followed by the patent number. The date shown may be the date the patent was granted or the date the patent application was submitted. Some inscriptions read only “patent pending,” “patent applied for,” or “patented.” For these, a search is possible only if the name of the maker is known and if the maker was also the applicant (in many cases it was not). Sometimes an object may bear a patent number corresponding to an application that was never granted. There may also be confusion among patent numbers, registered designs, and production numbers. In other words, a number on an object is not necessarily a patent number. Futhermore, some references to patents may be false, put there to discourage competitors.


Research into the patent for an object not only provides data on the date of the patent, but it can also furnish information on the inventor and sometimes on the material with which the object was manufactured. For example, let us take the case of a decorative object of American origin. The base of the box bears the patent number 505,462. A search of the U.S. Patent and Trademark Office's online database (">www.uspto.gov/), locates the original patent: “Manufacture of Celluloid Boxes” by A.C. Hafely and J. Redlefsen, 1893. The patent describes in detail the design of the object and the celluloid molding process (fig. 1). Thus, an examination of this patent will reveal that the box was made using a manufacturing system dated 1893 and that it was made from celluloid.

Fig. 1. U.S. Patent 505,462 by A. C. Hafely and J. Redlefsen on the manufacture of celluloid boxes

In other cases, however, the patent makes no reference to the material with which the object was made, as in the example of a banjo tailpiece bearing the inscription “Sept. 21 F&C PAT 1886”(fig. 2). The initials F&C refer to the American company Fairbanks & Cole (1880–90), which engaged in the manufacture of banjos and various banjo parts. As already indicated, searches for American patents from 1790 to 1975 can only be done online through the USPTO using two search criteria: patent year–number and current U.S. classification. It is easier to search using the patent number. Using the information on this tailpiece, the first step is to look for the patent numbers corresponding to 1886 by looking at patent–year number table. This search shows that the first patent of that year was numbered 333,494 and the last was 355,290. The next step is to look for the numbers of patents registered on September 21, 1886. The range of numbers registered on this date is 349,294 to 349,677. Finally, a search within this range (this is the most laborious part of the research) turns up patent 349,308, applied for by Frederick H. Hodges and entitled “Banjo Tail-Piece.” This patent provides a detailed description of the design and the manufacture of this piece but makes no reference to the material from which it is made.

Fig. 2. Banjo tailpiece showing its U.S. patent mark


The development of the semisynthetic polymers first began in the second half of the 19th century. Research was prompted by the need to find substitutes for such materials as tortoiseshell, ivory, and ebony, which were very expensive and impossible to produce on an industrial scale. By 1858, approximately 8% of British patents mentioned the words “molding composition” or “plastic” and related to compounds that reproduced the principal characteristics of such expensive materials (García Fernández-Villa and San Andrés Moya 2002).

Since patents do not always provide enough information on the material, research into other sources is needed. In the case of vulcanized rubber, Morgan (1991) is a good source; for cellulose nitrate, Friedel (1983), Selwitz (1988), and Reilly (1991); and for cellulose acetate and protein derivatives Kaufman (1963). Works relating to exhibitions are also useful: for vulcanized rubber, on the Great Exhibition of 1851 (Commission Française sur l'Industrie des Nations 1858) and on the Great Exhibition of 1862 (Chevalier 1862). In the case of cellulose nitrate, the works of Gerhardt (1854), Schmidt (1870), Jamin (1887), Worden (1911), and Baekeland (1914) can be recommended.

Table 1 lists some of the most important patents related to semisynthetic plastics. It has to be pointed out, however, that in the case of cellulose nitrate, euphoria over the possibilities this material offered produced a multitude of patents concerned with each and every possible use of this plastic (e.g., Ray 1865; Pierson 1867).

Table . Main Patents of Semisynthetic Plastics
Table .


Details contained in patents of the second half of the 19th century furnish useful information regarding the development of the first semisynthetic plastics. At that time, the means of producing them were entirely experimental, as the modern concept of the polymer did not exist until it was introduced by the German chemist Hermann Staudinger in 1920, and even then it was not fully accepted until 1930.

Yet, despite the lack of a firm scientific basis, researchers successfully improved the manufacturing process through chemical modification of the base biopolymer and the use of certain additives.

However, many of these materials were, as we now know, intrinsically unstable and were generally highly sensitive to ambient conditions (temperature, relative humidity, and light). This instability was due to the nature and proportion of the chemical groups (especially nitrate and acetate) of semisynthetic plastics embedded in the structure and to the presence of plasticizers. Such details are recorded in the patents, and therefore examination of these patents can be useful in cataloging artistic works or objects and in determining the measures best suited to their conservation.


Baekeland, L. H.1914. The invention of celluloid. Journal of Industrial and Engineering Chemistry6(2):90–91.

Chevalier, M.1862. L'exposition universelle de 1862 á Londres: Rapports des membres de la section français du jury international.Paris: Imprimerie centrale des chemins de fer.

Commission Française sur l'Industrie des Nations. 1858. L'exposition universelle de 1851. Paris: Imprimerie Impériale.

Friedel, R.1983. Pioneer plastic: The making and selling of celluloid. Madison, Wis.: University of Wisconsin Press.

García Fernández-Villa, S., and M.San Andrés Moya. 2002. El plástico como material de interés cultural (I). Aproximación a la historia y composición de los plás-ticos de moldeo naturales y artificiales. PH Boletín del Instituto Andaluz del Patrimonio Histórico40–41:87–102.

Gerhardt, C.1854. Traité de chimie organique (suite la chimie de Berzelius). Paris: Chez Firmin Didot Libraires.

Jamin, J. C.1887. Cours de physique de l'ecole polytech-nique III: Cours de optique. Paris: Gauthier-Villars.

Kaufman, M.1963. The first century of plastics: Celluloid and its sequel. London: Plastics and Rubber Institute.

Morgan, J.1991. Conservation of plastics. London: Plastics Historical Society.

Pierson, W. H.1867. Improved plastic compound made from vegetable fibers. U. S. Patent 65, 267.

Ray, G. W.1865. Improved water-proof collar and cuff. U. S. Patent 48, 239.

Reilly, J. A.1991. Celluloid objects: Their chemistry and preservation. Journal of the American Institute for Conservation30(2):145–62.

Schmidt, R.1870. Le développement des armes a feu et autres engins de guérre. Paris: Chez Tanera.

Selwitz, C. M.1988. Cellulose nitrate in conservation. Marina del Rey, Calif.: Getty Conservation Institute.

Van Dulken, S.1999. British patents of invention, 1617–1977: A guide for researchers. London: British Library.

Wohler, J. P.1998. Using patent numbers as a dating guide. Notes for Museum Workers 4. Ottawa: Pat Wohler and Associates.

Worden, E.1911. Nitrocellulose industry. New York: Van Nostrand.


Meickle, J. L.1997. American plastic: A cultural history. New Brunswick, N. J.: Rutgers University Press.

Quye, A., and C.Williamson. 1999. Plastics: Collecting and conserving. Edinburgh: NMS Publishing.


SILVIA GARCÍA FERNÁNDEZ-VILLA received a BA in fine arts in 1999 and an MA in conservation of fine art in 2001 from the Complutense University of Madrid. Since October 1999 she has been working in the Department of Painting Conservation of the Faculty of Fine Arts, Complutense University of Madrid, with a scholarship from the Ministry of Education and Culture. Since 1999 she has also been an honorary associate in the same department. Address: Universidad Complutense, Facultad de Bellas Artes, C/ El Greco 2, 28040 Madrid, Spain

MARGARITA SAN ANDRÉS MOYA received a PhD in chemistry in 1989 from the Complutense University of Madrid. Since 1990 she has been professor in the Department of Painting Conservation of the Faculty of Fine Arts, Complutense University of Madrid. Address as for García Fernández-Villa

Section Index

Copyright © 2005 American Institution for Conservation of Historic & Artistic Works