Well, finally, I've moved, I've unpacked all my stamp stuff boxes (over 45, I must be mad!), my study is still a mess but I'm trying very hard to refind some sort of working rhythm. Which isn't helped by the fact that I thought I'd written down something which I now for the life of me can't find anymore. So forgive me if I got the next thing all wrong as I'm working just from memory.
It has to do with Josef Hercik and his well-known Guernica engraving. The Czechoslovakian stamp was issued in 1966 to mark the 30th anniversary of the International Brigade's War Service in Spain.
It was well received to say the least. It won Hercik the Grand Prix in Naples and he even received a thank you letter from the painter Picasso himself!
But if I remember rightly Hercik himself was not too pleased with the end result and thought the quality of the printed stamp didn't do the engraving justice. Thankfully for him, the same engraving was used on a miniature sheet in 1981, to mark the 45th anniversary of the International Brigades in Spain and also to mark the birth centenary of the painter Picasso. Printing quality had by then very much improved, leading to a much more satisfactory end result as you can see here.