Fernando, first of all, I didn´t congratulate you for this beautiful piece before, but I do it now. It is a very nice piece of work.
Thank you for your comments about the silver work. It happens that I studied some silversmithing and have some intimate understanding of this craft. The silversmiths in some places of Latin América uses to make hilts and scabbards of chiseled silver in the same ways than in this badik is done. We make the scabbards, fill them with a special mixture of waxes and asphaltic resin, fixi the the scabbards in a box filled with the same mixture and then chisel them from above. I mean, the work is not done from inside, or it would be called "repousee". We make the volumes and the "levels" from upside. I checked with my friends, more experienced silversmiths, and they confirmed me this bandik and scabbard was only chiseled, meaning worked form above. But as Battara says, it could be better called "chasing", as the meaning of "chiselling" has another connotations in english. The point is that the work is done from above and not from the inside. I know what do you mean by a reposee type of work, but I think this is not the case. Please see this page, where you can find illustrations of hilts and scabards chased in this way, entirely form above with the scabbard already formed and soldered:
http://www.malamudorfebre.com/english/cuchillos-en.htm
And as you say, between steps the work is reheated and then suddenly dipped in cold water with some nitric or sulphuric acid, in order to soften the metal, the acid being useful to clean it´s surface.
Thank you for your attention
Gonzalo