Every collector should know the answer to this question: When were Biro pens introduced?

I am not going to tell you when. You can Google it if you don't know. The Biro pen was invented some years before it came into common use, and is named after its Hungarian inventor. Maybe you call these pens ball-point pens but Biros is what I have always called them

It's essential knowledge if you want to date documents, and especially if you want to check whether the dating of a cover is plausible in relation to the periods Before Biros (BB) and After Biros (AB) The cover below from a recent auction is definitely AB which is also the historical period of the envelope used, a 1960s (plus or minus) Soviet-style Mongolia Air Mail envelope. I can't read the date on the cancellation but you can be sure it isn't 1933 which is the date assigned by the auction house. It's also not Ulan Bator, is it, also the auction house's claim. I have once before seen these 1932 Mongolian stamps used late, like this. What I don't know is whether post offices started using them again at some point or whether Soviet-era East German technicians in Mongolia spiced up their letters home with philatelic frankings

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