I made note in the second post of the King Kirby 100 to an early proto-krackle effect Jack Kirby was using in what i believe to be Simon & Kirby's first co-credited work. That led me to wondering about the development of his stylistic Kirby Krackle, but far too immersed in preparing the KK100 to follow through on the pondering.
Happily, the Universe loves me in its weird way, and dropped Jack Kirby Collector #33 out of sequence in my path. Lo and behold - Shane Foley has contemplated this issue, and actually had the gumption to go digging. He found that, though we saw him playing with the notion back in 1940, The King didn't really define and embrace the Kirby Krackle we know today until a quarter century later.
Let's go to the stark comparison he provided bracketing that period - these two Silver Surfer covers for the Fantastic Four, just two years apart:
From nary a trace on FF #50 to fully embracing the Krackle on FF #72. And what a dynamic difference it brings to the background. Shane further traced the evolution of Kirby's experiments as he worked out the fine details of his famous patterned dots over the course of 1966. He provides us with this nice visual chart of the progress:
Once Kirby decided to develop the effect, it took him remarkably little time to refine it and incorporate in seemingly endless ways, adding yet another layer of dynamics to his work.
Shane Foley leads us to the Krackle in Jack Kirby Collector #33 (2001)