[Georgia]

Hi Alan - we must have been writing the last post simultaneously, so I just missed yours! Thanks for your reply, I think that's a very valid point you have made about the possibility of corroding iron releasing arsenic from the patination layer; the blade I tested which had the strongest result certainly had a powdery whitish-grey residue on the surface and the blade itself was not in the best condition. However, the other blade with a strong positive was in a much better condition and did not have much in the way of surface residues, in fact the only reason I chose it from the 40-odd keris in the collection was because it of one of the darkest and most obviously stained. The sample I picked from its surface was an oily sort of gunk from along the gonjo.
Regarding the possibility of arsenic being present in the iron, that is definitely a possibility (I think arsenic is one of the main trace elements found in iron), but I don't know if it would be there in large enough amounts to be picked up by the Merck test. In any case, the samples collected were of the residues and not the metal itself, so I don't think this is very likely.
One other possible cause is the 19th century museum practice of slathering collection items with arsenic to kill pests - although this was usually confined to natural history/organic collections, perhaps someone decided it would be worth it to protect the handles and sheaths?
My project's coming along steadily, I'll send it to you in the next few weeks to have a look. Got five more weeks til it's due! Thanks for your help.
G