Just looked at your page and this looks interesting. I am not however aware
of any particular limit on the number of grey shades on photogravure on
copper. Though I'm only a beginner the second one I did last week gives
quite a good impression of continuous tone.
Peter Marshall
On Fixing Shadows, Dragonfire and elsewhere:
http://faraday.clas.virginia.edu/cgi-uva/cgiwrap/~ds8s/Niepce/peter-m.cgi
Family Pictures & Gay Pride: http://www.dragonfire.net/~gallery/