Chickens generally lay more eggs at some times of the year than others. Historically there was a plethora of eggs during the Spring, and they could be purchased very inexpensively – and eggs were much scarcer and more costly during the winter months.
As a result, people often preserved eggs using the water glass method. They mixed water and water glass (hydrated lime) together in large stoneware crocks or jars. Eggs were then placed in the liquid to preserve them.
According to a 1920 advertisement by the Stoneware Manufacturers Association (who would have guessed that there was a Stoneware Manufacturers Association) which represented the manufacturers of the crocks:
Eggs properly preserved in stoneware jars will keep fresh as the day they were laid for 8 to 12 months.
When I googled water glass eggs, I discovered that some people still use this method to preserve eggs. For example, Homesteading Family and Timber Creek Farmer each have posts about how to use the water glass method.