The Thonet No. 18 chair was designed by Gebrüder Thonet in 1876. This chair was manufactured by Jacob & Josef Kohn (J & J Kohn, father Jacob and son Josef) around 1900 the biggest competitor of Thonet. The firm worked with designers of the Wiener Werkstätte (amongst others Josef Hoffmann en Koloman Moser). Marked underneath the seat with paper label: "Jacob & Josef Kohn, Wien". This piece has an attribution mark, I am sure that it is completely authentic and take full responsibility for any authenticity issues arising from misattribution