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INTRODUCTION:
Dating scientific instruments is sometimes straightforward, and sometimes not. Rarely, a maker would date his instrument. A good example are the microscopes made by Powell & Lealand. In many cases, where serial numbers are known, lists exist of either the exact date of production or an approximation that is close can be made based on others with known dates. The address of a maker can be helpful, particularly when they moved and the years at different locations are known. Sometimes catalogs, which are usually (but not always), dated will be helpful in identifying the approximate date of an instrument. Advertisements are often very valuable as these can be used to date instruments. In some cases there is simply no easily found way and some other facts are helpful such as those presented on this page. Dating can be more of an art than a science at times, and this art is far from perfect! I have witnessed many advanced collectors miss the date of an instrument based on impression instead of facts. As time goes on, I often find myself redating some of my instruments as new information becomes available. Sometimes the facts below are helpful in at least dating to a period of time. For instance, a mystery object with a U.S. postal code must date to 1943 or later. Occasionally a patent number will help to date an instrument by its patent date. It is beyond the scope of this page to give specifics on dating, but I hope this is a good introduction. The reader should be aware of certain valuable references such as the Directory of British Scientific Instrument Makers 1550-1851, by Gloria Clifton. One should also NOT accept casual references to dating such as can be found in certain publications and the Web. An example is the catalog of the Billings Collection in Washington. Although a lot of the information in the Billings catalog is useful, there are many errors in this catalog both as to maker and to date. For globes, a list of the dates of countries is often very useful. For instance, Israel was formed May 14, 1948. If a globe shows Israel as a country, that globe must date to after its date of formation.

For a table of dates useful in trying to date antique globes, please see the globe dating page. Some of the terms included here (such as S.G.D.G),just do not help much with dating as their use spans such a long time

1. Brevete´ : Patent (French)
2. 'MADE IN'
   This is the Country of Origin or COO. It was required by the McKinley Act in the USA starting March 1, 1891. It is unclear how many makers followed it at that time, but certainly not likely before that date. This can be helpful but occasionally some makers, proud of their heritage, may have labeled their products with the COO before the McKinley act.
3. NICKEL SILVER OR GERMAN SILVER:
   Nickel-Silver, a brass alloy with a silver-like finish, was invented in China and its first European mention was around 1600. The finer quality Nickel Silver process was introduced from Germany to England in 1830. Some microscopes, like an example of the Penny Cyclopedia microscope by Ross were made mostly of this alloy. As this alloy ages, it develops a slightly dull finish, as opposed to real silver or silver plate which becomes more grayish and eventually blackish. An example of a small microscope made mostly of Nickel-Silver is the Browning 'New Miniature Microscope'.
4. USE OF NICKEL, CHROME, AND RHODIUM PLATING
   Nickel plating was occasionally used in England as early as 1837 when it was invented by Golding Bird, but the first use in construction of microscopes was likely quite later. The first nickel plating done in the USA started with a process in 1869, but this process did not become popular in the USA until the last quarter of the 19th century and reached its peak after 1915. Chromium plating was invented in Germany about 1925 and was not frequently used initially. Rhodium plating became commercially available in the early 1930's and was used on Wollensak Microscopes; apparently it was simpler to plate with Rhodium at that time than chromium. An American patent for that process dates to 1932. Ironically at the outbreak of WWII, rhodium use became restricted to military applications. Today Rhodium is a very valuable rare element and its use in plating is mainly restricted to Jewelry. Nickel plating usually does not tarnish as much as Nickel-Silver, but will tarnish somewhat eventually, unless protected by lacquer or another overcoating. The drawtube of the Spencer No. 1 microscope of c. 1900 is a good example of the use of nickel plating on a microscope.
5. USE OF BAKELITE
   First invented in NYC in 1907
6. D.R.G.M. German registration system introduced in 1891.
7. DEPOSE- French registration system started sometime before 1900 but I have been unable to get any more information.
8. S.G.D.G.: abbreviation of "without government guarantee," was in France a legal term releasing the State of any responsibility on the effective functioning of the patented device. This was established by the Law of 1844, which provides that patents are granted "without prior examination, at the risk and peril of the plaintiffs, and without any guarantee of actuality, novelty or merit of the invention, fidelity or accuracy of description ". This term disappeared in 1968. In Belgium, according to Art. 22 of the Patent Law of 28 March 1984, the SGDG principle is still applicable.
9. POSTAL CODES:
   LONDON: WC, N, SE etc from 1857-8
   ENGLISH WC1, WC2 1917
   US POSTAL number code: 1943
   US Zip Code: 1962
10. USE OF THE LONG S AS IN Rofs:The use of the long S (f) was abandoned in printing in the early 1800's, but in cursive writing and engraving its use continued at least into the 1830's and in some cases beyond. For example it was used on some Plossl & Co microscopes into the 1870's.