Antique Moro Gunong

[kai]

Hello Ian,

Alloys with small amounts of gold can certainly oxidize, but I think it is the copper or silver components that are most affected by the oxidation.

Yes, in gold alloys it is the "lower" metals which oxidize while the gold is quite inert in such a setting.

However, alloys can exhibit quite a few funny/weird characteristics which need in-depth research to really appreciate them fully.

Regards,
Kai

[Battara]

I too Ian, my kris that once belonged to Datu Piang that has a solid suassa hilt (with solid yellow gold accents) was once black! I thought it was silver until I polished it and found the solid suassa.

What I base my leanings on the metal is the type of hue in its cleaned state, which looks to have less gold and more silver. Ian I think this is more like samrit than suassa.

Either way, it is a nice piece!

[Ian]

That's interesting Jose. For these non-silver black oxidized pieces, I wonder if there might be some arsenic also in the mix. Some oxides of arsenic can be very black in appearance. I seem to recall that arsenic has some mystical properties in mainland SE Asia--certainly some of the Hmong who live in the Twin Cities used arsenic for medicinal purposes and I was told by members of that community that arsenic is a powerful substance in their culture.

Ian.

[David]

That is a beautiful and elegant old gunong you have there Fernando. Amazing how many luks were fit into its 19cm length. Very nice work there. Also a very nice restoration on your part.

[Battara]

That's a good question Ian. I don't know for sure. I know Bali uses arsenic in etching their keris blades.

One thing is for sure - often even the copper/gold mix of suassa has some silver content in it so that it won't become too brittle to work. Although copper is incredibly soft, when mixed with other metals it makes the new alloy brittle.

Also, some used the silver/copper alloy in a particular mix to LOOK like copper/gold suassa (especially since gold is so expensive).

[kai]

Hello Ian,

as mentioned by Jose, most suasa also contains silver and it will be mostly silver sulphides contributing to any very dark patina.

For these non-silver black oxidized pieces, I wonder if there might be some arsenic also in the mix. Some oxides of arsenic can be very black in appearance.

At least the 2 common oxides of arsenic are white.

It's the arsenate salts with metals like iron that are blackish (cp. warangan). Metallic arsenic in an alloy is a quite different kettle of fish though and unlikely to be more than a trace contaminant...

I seem to recall that arsenic has some mystical properties in mainland SE Asia--certainly some of the Hmong who live in the Twin Cities used arsenic for medicinal purposes and I was told by members of that community that arsenic is a powerful substance in their culture.

Yes, arsenic compounds like realgar have been utilized in TCM (Traditional Chinese Medicine) for millennia and have a scientifically proven track record in modern medicine as well. However, there also are cancerogenic effects known...

Regards,
Kai

[Ian]

Thanks Kai.

Yes, it's arsenates [–AsO4(-3), etc.] not oxides of arsenic [As2O3, As2O5, etc.] that are black.

I'm not sure that silver oxidation explains the intense black oxidation that I observed on my samrit covered daab. Some time ago I was sent an old formula for samrit, and no mention was made of silver in the mixture if I recall correctly. Also, the intensity of the black color was much more than I see on silver covered pieces from the same general region--silver oxidation tends to be more grey than black.

I have another Lao daab from the 17th C with a samrit hilt that has virtually no oxidation, and I have no explanation why one would have such a dark patina and the other virtually none. Presumably it reflects different components in each sample of samrit.

[Battara]

Actually for silver the longer the oxidation the blacker it gets.

Another consideration is the copper content, because when copper is involved, then the darker the oxidation gets as well. Copper often gets the green/blue/even multi-color patinas. However, when mixed with certain metals, the patina might change depending on the metal mix. Copper/tin mixes (bronzes) may yield a green patina, but can also give a dark brown to even black patina. This black patina can also be seen on silver/copper mixes where the mix has a large percentage of copper (in fact, silver/copper mixes with large amounts of copper often patina quicker than either silver or copper by themselves! ).

Hope this is now clear as mud...........

[Ian]

Thanks Jose.