There is a sector of the paper banknote / currency market that defies understanding by most collectors - error or variety collecting. This dedicated group of collectors actively seeks out paper (and polymer!) notes that demonstrate each of the many and varied errors that can take place during the production or printing process.

There are missing print phases overflaps, wet ink transfers, mismatched serial numbers - the list goes on! I have always wondered why someone might want to collect the product of what is patently someone else's mistake (if only we could all sell our mistakes, people would queue up to join the school of hard knocks), and firmly believe that the collector of error notes has more in common with a fetish fiend than they might like to admit, but that's another story altogether...

News has just come out of the US of a whole new type of error banknote - an "Obstructed Plate" error, which is of course part of the broader group of "Process Errors". This particular printing error had part of the printing plate obstructed by a paper clip, resulting in what is a truly incredible error.

According to Steve Sullivan’s U.S. Error Note Encyclopedia, this note and a companion note with a similar serial number, represent the ONLY two examples in which a recognizable foreign object is completed inked and stamped (resulting in the object being embossed) onto a piece of United States currency.

The result, according to Mr. Sullivan, is that the “raised impression of the Paper Clip has been inked” making the Paper Clip appear to be “part of the face plate design.”

Just how much is this new note worth? I'm thinking more than US$40,000 if the website of the dealer selling the note is anything to go by. Apparently, "Process Errors ... are valued in [Sullivan's] Encyclopedia at upwards of $40,000."

That's certainly a lot more than any Australian error coin or note has sold for that I'm aware of!

I vaguely recall seeing an error coin from the US that had a foreign object bonded into the metal through an error in the production process, however I've certainly never seen an Australian coin or note that has a foreign object bonded into it.

I have seen some pretty crazy errors in both coins and notes - completely blank notes and coins that've been struck on the wrong type of metal (planchet), but never anything like this.

What's the most extreme error you've seen?