I'd like to attempt to make a contrast reducing mask for a color negative as described by Ctein in his book "Post Exposure." He recommends using Tmax 100 film developed in a special developer that produces a thin, but still color neutral, negative. The developer formula calls for potassium hydroxide, which I don't have, but I do have sodium hydroxide and am wondering whether I could substitute? I know nothing about chemicals, but see that the two of these are listed as "closely related" on a couple reference sites.

Also, if anyone has experience making masks for color film, either by Ctein's process or an alternative, I'd sure appreciate any tips.