This egg is not sterling by any stretch, but I posted it just as a record of using this technique, which btw I will likely abandon. I just painted some half-egg shells washed after cracking (for breakfast) and dried them and painted the outsides with fingernail polish abandoned decades ago by my daughter.
What is curious is that the fingernail polish changes the way the egg shells break, kind of an interesting twist. Anyway, the previous way of getting colored egg shels was using pysanky dye but that fades with time. Markers are ok but they leave the white edge around each piece (as does using fingernail polish) so these are just issues with this medium. I do like the egg to be black (in this case it was a brown egg shell and I did not change the color) as that gives it a stained glass, or mosaic, or tiled look.