As far as I understand normal cooking will create additional seasoning layers, and a cast iron skillet will get better with time. But if I only rise the temperature high enough to cook food (and not high enough where I see smoke), how does polymerization actually happen?
I thought that if there was no smoke, then polymerization was not happening, but is that the case?
This article takes a pretty good dive into the science of seasoning, but the long story short is, polymerization is basically always (slowly) happening in oils. “Drying” oils polymerize “better” than others, and polymerization is accelerated by things like heat, light, and most significantly the release of free radicles (aka smoking).
When you cook oils with your cast iron, some of those oils will polymerize and bind to your existing seasoning.