It took a very long time for collectors to discover what had happened.
The corner supports with the shelf member fit on the post supports in wedging engagement therewith to thereby horizontally locate the shelf member for the desired vertical height. A series of continuous electrical discharges passing through the wire removes the metal; the wire doesn't contact the steel directly. The 1840 Penny Black might well be the most famous stamp ever produced, it being the 1st pre-paid postage stamp.
