Ward, I appreciate that acid should chomp through rust just as it will cause the appearance of the watered pattern by removing some of the softer iron. What I still worry about is whether the effect will be what I desire. To give you an idea of why, I discussed
in an earlier thread the effect of Renaissance Metal De-Corroder on the watered steel of this barrel and various other objects. The results were varied. Rust went, but so did lustre, and I find myself unsure of whether repeating the process - bearing in mind that this stuff is, as far as I can tell, an aqueaous solution of hydro-oxycarboxylic acid - is a good idea.
Some pics, herewith, of the areas of this barrel I treated with this acidic solution. The pattern remains visible, one way or another, but in the tang area (which was subjected to the longest treatment) the shine has vanished from the steel. A consequence which, along with the low visibility of the pattern, I wish to avoid.