Achim Weihrauch
Ursprung und Entwicklungsgeschichte des indonesischen Kris. Historische und metallurgische Untersuchungen.
[Origin and development/evolution of the Indonesian keris. Historical and metallurgical studies.]
Basel, 2001.
This is a Ph.D. dissertation in German; 480 pages with a lot of interesting pics!
The writing style is academic and may be tough to read if your German is not top notch. I've tried some online translators but none seemed to work reasonably well, even when breaking up complex sentences. If you want to dig into the text, it might be worth to install a professional translating program (some offer a free demo) and also replace the inevitable mess-ups throughout the document (e. g. the plural "krise" equals the German word for crisis).
Regards,
Kai