Quote:
Yes, someone thought it was a good idea to have a percussion cap in a stamp so that when you hit it with a cancelling device, the cap would blow a hole in the stamp, preventing reuse.
The Chinese were way ahead of everyone, they simply made the outer ring of the CDS (Circular Date Stamp) with a
Knurled finish.
(Same as the US Grill )
When the hammer was struck, the diamond points broke the paper
and the cancelling ink infused.
Never understood why that never caught on.