jo - about books with gemstone/jewelry rendering, one i have is sylvia
wicks’: ‘jewelry making manual’ BUT when you get to ‘design
presentation’ in the ‘design elements’ chapter, make a note that the
headings on OPALS & COLORED STONES: INK METHOD are switched - they
have the colored stones title above the opals (one of my
specialties). also, i’ve found it best to work wet into wet when
rendering stones with any schiller/fire. & it’s a good idea to
’finish/clean’ your lines with very sharp prismacolor or even swann
pastel pencils & some applicable templates after all your
illustrations are dry - this book isn’t exhaustive on rendering, but
it’s a good start. good luck - ive