A review of some elements for the history of mechanical twinning centred on its German origins until Otto Mügge’s K 1 and K 2 invariant plane notation

There is a specific nomenclature for the so-called mechanical twins or twins obtained by mechanical deformation. This nomenclature, (K1, η 1, K2, η 2), is due to Otto Mügge in 1889. The German mineralogist and crystallographer Mügge (1858–1932) rationalised twinning observations made by himself and by other German scientists since 1859 such as Friedrich Pfaff, Heinrich Wilhelm Dove, Eduard Reusch and Heinrich Baumhauer, not to forget a formal contribution by William Thomson and Peter Guthrie Tait noticed by Theodor Liebisch who informed Mügge about it, and further classifications by Arrien Johnsen, one of Mügge’s pupils. The presentation of this scientific development also mentions the medieval alchemist Pseudo-Geber and the Renaissance metallurgist Vannoccio Biringuccio who ‘heard’ the cry of the tin now known to be due to deformation twinning, the first models of progressive twinning involving some local atomic rearrangement, with Woldemar Voigt in 1898, Yacov Il’ich Frenkel and Tatyana Kontorova in 1938 and the first drawings of a twin(ning) dislocation by Vladimirskii in 1947 and by Charles Frank and Jan van der Merwe two years later.