I found some small bit of information on an engraving place in St Petersburg but possibly more commercial than you are talking about.
I have bought two eggs that haven't arrived yet. One I hope is antique Bohemian? overlaid glass - I'm waiting to see what arrives but it doesn't matter whether antique or not as it was bought to try and help with identifying my pink (cranberry ish) overlay goblet. It is coming from America. I'm curious - the pattern is very similar to Boston and Sandwich pattern so it will be interesting to see it - may be antique Bohemian, maybe new Ajka, maybe Boston and Sandwich - the pictures were very bad hence I'm not entirely sure what's arriving or even what colour (if it ever arrives).
The other I think it's old as in very old (or rather I'm hoping it is, fingers crossed here

it might well be made a few years ago - again terrible photos). It has really pretty engraving. It's a very different style to my clear egg at the start of this post but I have to say I love my cathedral egg. It's beautifully done.
m