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. 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.

If the patent number and year are known, photocopies of the patent specifications can be procured through the British Library Document Supply Centre ([email protected][accessed July 27, 2005]) or the Leeds Patent Information Unit ([email protected] [accessed July 27, 2005). Patents from 1790 through 1975 are searchable only by patent number and current U. classification and only images of these patents are available. Many of these old patents are not yet accessible online.

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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. British patents registered between 16 originally lacked numbering and were not published.

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. 1870 would be from the United States, for example, but if c. 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. This format was maintained up to number 14,359 (no.

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 18, 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).

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 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.