I know the things you've mentioned.

I've found a book from 1849 (?), the flower petal tinctures were described there. Quite old technique.

And bichromate solution after exposing will also make an grey-green image (not washable, but pale).

I have not checked the egg properties and hopefully I'll try this in summer. Now we have almost no sun here. I'm feeling it's close to the North Pole from here, this winter seems to be endless.

Cheers,
Luke