I forged a boot dagger out of crane cable last night. You get a nice pattern with wavy lines indicating strands. Its not as high contrast as say 1095 and 15n20 but its a nice pleasing pattern to me.
Surprisingly I have found that the amount of rust you begin with doesnt seem to effect forge welding it. As with all junkyard steel you really ( at least in my case) dont know what you have steel wise. Id like to try some with a known product but I dont have a supplier near me that I know of.
I use 50/50 distilled water and Ferric Chloride (radio shack). I let it sit for a minute or so... when the black buildup collects, take it out... windex to neutralize....OOOO steel wool... clean then back in until I get the desired etch....
I think using clay for the hardening is excellent..... Looks great.... If you leave the blade in too long... the black oxidation will cause the softer steel to etch faster than the hardened part of the blade...and can cause issues visiably... Careful about brass guards soldered on the blade then etching.... the brass gets into the contours of the cable much easier than random and so forth.... or sometimes so it seems.... you might like this coloration...????