The oldest known periodic table has been restored after a major conservation effort. Discovered in 2014 at the University of St Andrews' School of Chemistry by Dr Alan Aitken during a clean out of old stores, the classroom table of chemical elements dates from 1885 and accurately reflects the level of knowledge at the time of its printing.

The periodic table of elements is well known to any student who has sought visual relief in classroom posters during a particularly boring chemistry lecture, but it is also one of the most remarkable attempts to organize a set of facts in the history of science.

Though there have been several attempts to create a table of elements going back to 1789, it wasn't until Russian chemist Dmitri Mendeleev published his in 1869 that we first see the periodic table as we understand it today. Though there are a number of different ways to present the periodic table and all of them have a strangely irregular appearance, the relationships between the elements and their properties that formed the basis of Mendeleev's table produced a remarkable discovery.

Scientists found that the way the periodic table is organized isn't arbitrary. In fact, it is a reflection of objective reality. By finding where an element fits in the table, a chemist can, without even having a sample of the element, tell if it is a metal, a noble gas, an alkali metal, as well as a great deal about how it will interact with other elements. In addition, it was possible to deduce the properties of elements that hadn't been discovered yet due to the gaps they filled in the table.

It's this last fact that helped scholars to date the St Andrews periodic table. According to the university, the table is similar to the second version that Mendeleev drew up in 1869, but there are discrepancies. Gallium and scandium, discovered in 1875 and 1879, respectively, are included in the table, but germanium, which was discovered in 1886, is not. This corresponds to an inscription on the table, which reads, "Verlag v. Lenoir & Forster, Wien." referring to a Viennese scientific printer that was in business from 1877 to 1888. The purchase was made by professor of Chemistry Thomas Purdie, who had a strong interest in the rising field of organic chemistry.

When it was found, the St Andrews periodic table was in a shocking state after many decades of neglect. The paper was fragile and brittle due to oxidation and acidic wear on the fibers – not to mention its being rolled up and bearing the weight of a heavy linen backing.

Under a grant from the National Manuscripts Conservation Trust (NMCT), special collections in collaboration with Richard Hawkes from Artworks Conservation undertook a grueling conservation effort. According to the university, this involved brushing away loose debris, taking off the linen backing, washing the chart in neutral-pH deionized water, deacidification using a bath of hydrogen carbonate, repairing it with Japanese kozo paper and wheat starch paste, and rehousing it properly under controlled conditions.

Because the original is too fragile for public display, the School of Chemistry was provided with a full-size facsimile.

"The discovery of the world's oldest classroom periodic table at the University of St Andrews is remarkable," says Professor David O'Hagan, recent ex-Head of Chemistry at the University of St Andrews. "The table will be available for research and display at the University and we have a number of events planned in 2019, which has been designated international year of the periodic table by the United Nations, to coincide with the 150th anniversary of the table's creation by Dmitri Mendeleev."