Ever wonder what fractionation is?
It basically means taking the plaintext character and enciphering it with a cipher that generates a multi-character replacement for the symbol.
Sort of like X = YZ.
The value comes in being able to manipulate this ciphertext with another cipher method such as transposition. Move, separate and jumble Y and Z by some set method and it will be hard to recover the plaintext.
Fractionation is little more than a category of substitution ciphers, the ones that give you more ciphertext than plaintext. That’s it. It’s only really effective when used in combination with something else.
This is important for Kryptos because it is very possible that this sort of fractionation/cipher combination was used in K4. One drawback is that it implies that the final message of K4 is less than 97 letters which is short enough already. An argument could be made that K1-3 have used methods that allowed 1 character of ciphertext to decipher to 1 character of plaintext and that it is unlikely that Sanborn would change that. It’s also plausible to argue that it’s hard to make a message of 40-60 letters that will fit into the whole sculpture and provide impetus to solving the final message.
As a relatively common and widely used phenomenon, it would be foolhardy to not consider it and possible applications of fractionation that might have been used in K4.