Gordon,
Don't know about using sodium silicate or sealing them in lard, but if kept cool (under 45F or so), eggs last A LOT longer than we think. Sealing them in lard/fat would keep oxygen away and therefore keep bacteria at bay, just like in potted meat.
A month is not uncommon. 2 months is not rare. In restaurant kitchens, we can tell by certain things. If you are poaching eggs and the whites in a certain batch aren't coagulating well, it's likely they are getting old. Taste-wise, I've been able to tell no difference.
But these days, going through 60dz eggs a week, they never stay around long enough to test any theories!
Mario