Please elaborate on this point, as I don't fully understand it.
When I read through the archives, and various metalworking books
there are many references to polished tools but I have not found a
full explanation why.
I am going to have to go into fundamentals to explain why it is
Take a square sheet of copper, let’s say 4 by 4 inches and place one
blow in the center. Hammer of punch - does not matter. Then, using
small metal rod, examine square for sound. What you will find is that
metal structure changed not only where you placed the blow, but whole
square was affected, more towards where the blow is, and less towards
Place another blow away from the first one, and examine again. The
pattern will be more complex, and there will be an area between two
blows with distinctly different sound. That is the area where metal
was affected equally with both blows. You will find that even if you
never touched that area, the level of work hardening could approach
the area been stricken. If two blows are close apart, it may
actually exceed it.
Imagine doing it over and over again, all over the metal you are
working with. You will be creating knots of extremely overworked
metal, which no annealing can restore, because micro-fractures
already developed. It is only a matter of time before such metal will
When tool surface is not hardened and polished to perfection, this
effect is magnified, because of different friction zones of the tool
surface. If you place a blow with such tool, it will pull the metal
from surrounding area differently. That will create a knot or knots,
between different zones of metal flow. So the phenomenon of knots
formation is magnified by the factor of how many different friction
zones your tool has.
In the book "The Jewelry Engravers Manual" by Hardy and Bowman
this statement is made: " a brilliant cut depends on the brilliance
of the polish" The book goes on to state that the two belly faces
of the graver must be polished, then states "acquiring a high
polish on the face is generally detrimental to good results". Why
would only two faces polished on a graver be better than three
polished faces ? There was no technical explanation, so I did not
The answer to engraving question is somewhat similar, but different.
The belly must be polished because different zones of friction
create the same type of knots ( I am only using the term for
convenience ) on the surface of the graver. Steel can be overworked
in exactly the same way. Also graver can become “locally annealed” if
friction is sufficiently high.
The face of a graver is not polished because of impossibility to
maintain cutting edge. This is simply a limitation of technology of
sharpening. An attempt to do so, will result in rounding of cutting
edge and that when graver is starting to slip.