Unusual Etch on a Moro Blade

[delor]

I agree with mross. The "random" pattern is the proof of a laminated construction.
If there is no sign of lamination between the edge and the first brown line, this could possibly be a sandwich construction with central single steel (not sure, according to your two last photos which seem to show uniform lamination on the whole blade).
A good reason for sandwich construction is that a combination of non "quench-able" materials (ie : low carbon steel and nickel) was often used for lamination, in order to get good etching contrast (steel goes dark grey and nickel remains bright). If the laminated material canot be correctly hardened, this leads to sandwich construction which allows to have some good steel at the edges. Also good steel was much more expensive in the old days than common iron, so the less steel used the better it was for economical issues.
I cannot say what are the materials used for the construction of your blade. Might be iron + steel...