Let me differentiate between "etch", and "stain".
If we etch something, we bring up the topographic relief that is revealed when the acid eats away the softer metal.
If we stain, we apply a substance that will reveal the colours of the differing materials in a blade.
Before attempting to stain a blade we must clean it of rust and dirt. A gentle fruit acid such as pineapple juice is a very effective cleaner, and will also very lightly etch.
When we look at an old blade we can sometimes see lines in the blade that look as if they may be pamor, however, with many old blades we are not seeing pamor, we are simply seeing the weld joints caused by the folding process used in cleaning the material before it was forged into a blade. You can sometimes see these weld joints in old European pieces too.
Sometimes with an older piece of wesi aji, a soak in pineapple juice will not only clean the blade, but will also reactivate the latent arsenic from previous applications, and you can get a half-way acceptable blade finish by the use of the pineapple juice alone. You may find that this could be the case with the tombak you have shown.
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