I remembered seeing this stamp, 1969 Repin 10kop value with Hovest guarantee for sale on German eBay years ago. Michel 3653y, price -.- In regular Michel 2009, it's the only one I can see from the 1960s being listed.
It would appear this is one of the UV paper stamps I have. Among many others I have now discovered, since I started to study them this month.
I've never really found a good explanation on how Soviet stamps were printed and reprinted during 1960s. I think I had read they were printed in different places but I'm curious if it applied for the same issue or did printing workshops just change over the years.
It's still interesting that one set can have some stamps on UV paper and others on normal paper.
Anyone know more about this subject? Anyone know if new Michel Spezial has more of papier fl. varieties listed?