Nice Pair Of..................

[njsteve]

The basic principal is that when metal is stamped, the stamp compresses (stresses) that section of metal in forming the visible image of the letter/number. Decking the block removes a thin layer of the metal but does not relieve the original stamped (stressed) area. Therefore, by using a heat process or acid and electricity process, they can get a ghost image to appear on the surface of the metal that appears for a long enough time to photograph it. If you stamp over that area, you altered that preexisting compressed area of metal and destroyed it.

Here's some light reading on the subject:

http://lucy.mrs.org/2006brazil/wedpix/j502.pdf

http://cms.ucok.edu/chemistry/Vonmin...%20Lecture.pdf