Coasters
https://www.oed.com/dictionary/coaster_n?tab=meaning_and_use
https://britishbeermats.org/beermats/beermat-history/
https://scholar.uwindsor.ca/cgi/viewcontent.cgi?article=1020&context=llcpub
Kenneth Osborne and Brian Pipe, The International Book of Beer Labels, Mats, and Coasters (London 1979)
https://stompstickers.com/blogs/articles/history-of-the-drink-coaster-who-designed-it-why
