no mechanical assist - acid etching - or photoengraving --
  Why authentic hand engraving? The many years required to develop the hand and eye coordination necessary for traditional hand engraving cannot be avoided.  Electric powered or compressed air "engraving" tools wedded to a 20x micrcroscope will cut a lot of very narrow lines with a minimum amount of skill required by the operator.  While these types of mechanical  assist engravings when executed by good artists sometimes take very good photos, they may seem lacking when viewed "in the hand". 
  The claim that employing an electric or air powered tool is "hand engraving" is inaccurate from the perspective of the general public.  For example, "hand polished" is not the result of polishing using a polishing wheel because the part is held in the hand.
  Some non-traditionalists use photo-engraving whereupon a little acid resist, prepared film and light will instantly give a highly detailed result.  The operator can deepen a few lines here and there over the photo-engraving with an air impact tool to improve the depth of some of the shallow etched lines.  In some cases the engraved lines are still not deep enough so the operator/engraver rubs black ink into the engraving to better define it so that it takes a good photograph.
  Acid etching, stamped engraving, and plating are valid methods for creating beautiful designs on firearms but,  traditional hand engraving using the time proven techniques of a hammer and chisel always achieves a more authentic and better result for most of us.
  William Morris (father of the Arts and Craft Movement) put this issue to rest over 100 years ago:

Welcome to our world of gun dogs and gun engraving. Our karma is
our faithful dogs,
the excitement of the flush,
the  beauty of figured wood,
gold on polished steel.
and clean engraved cuts forming lines of beauty.
For some of us
these are the things of love and art in our lives
                      that bridge heaven and earth.                                        STEPHEN
The hammer and chisel with the hand burin are the only tools used for true hand engraving
"Set yourselves as much as possible against all machine-work
(this to all men). But if you have to design for machine-work, at least let your
design show clearly what it is. Make it mechanical with a vengeance, at the same
time as simple at possible.
Don't try, for instance, to make a printed plate
look like a hand-painted one: make it something which no one would try to do if
he were painting by hand, if your market drives you into printed plates: I don't
see the use of them myself.
To sum up, don't let yourselves be made machines, or
it is all up with you as artists
no man is so clumsy or base a workman that he is not fit for something better than
that. " ("that" being the use of machines to replace hand work.)
From Art and Beauty of the Earth , by William Morris