The button is of Yum-Yum from the widely popular 1885 comic opera The Mikado by Gilbert & Sullivan. An English fascination for all things Japanese spread through the country as trade between Europe & Japan increased dramatically from the 1860s - 1870s--as found here: Geisha button, Japanese ladies with umbrellas. - Allie's Adornments
Don......
Thanks very much for the info, much appreciated. I wasn't sure what year it from or anything about it as it was found beside a 9th century ring forth in Kildare Ireland.