Colorit or Novorit substitute

I want to fill some parts on my 10K & Sterling rings with black
"material" I can polish the colorit perfectly(shiny), but is very
expensive, theres another alternative??? Should I change to vitreous
enamels?? Sometimes we have to produce 3000 rings every week and
after doing numbers, Colorit is not a affordable choice.

Thanks
Alberto Covarrubias