@liminal DarkScribe what kind of material is egg glass?
It is a water soluble lacquer – a sodium/potassium silicate mixture. Eggs were dipped in it and allowed to dry – it made the shell air-tight. Eggs shells are normally oxygen permeable. (It is also known as “Water Glass” .)
From Wiki.
Food preservation
Sodium silicate was also used as an egg preservation agent in the early 20th Century with large success. When fresh eggs are immersed in it, bacteria which cause the eggs to spoil are kept out and water is kept in. Eggs can be kept fresh using this method for up to nine months. When boiling eggs preserved this way, it is well advised to pin-prick the egg to allow steam to escape because the shell is no longer porous.