WN: How many cryptographic processes are used on the sculpture?
Scheidt: There are four different processes. Two of them are similar and the other two are different things. The first three processes were designed so that a person could, through cryptographic analysis, have access to the English language (on the sculpture). And the last process, I masked the English language so it’s more of a challenge now. It’s progressively harder in the challenges.
(WIRED Interview, 01/21/05)

Well this seems pretty straightforward.  I bet James was pissed that Ed explained this much.

I think we know which two are similar (K1 and K2) so I guess the other two are different things.

FYI, this would suggest that K4 is all 97 letters and isn’t two short ciphers giving the Copperplate 5 “processes”.  This statement is one of the biggest reasons I don’t think K4 is like K1-3 at all.  Vigenere-vigenere-transposition-what?

How exactly would one go about “masking” the English language?

He seems to describe this so casually but I’ve never heard anyone give a satisfactory explanation for how he would have done this.