Sciencemadness Discussion Board

Pattern welded metal and etching

kuro96inlaila - 23-3-2018 at 22:22

Okay before we start on the discussion I'd have to make clear I don't have any pattern welded metal on hands, so I'd not be able to test any of the reaction on it.

In malay culture, the pattern of keris dagger is made by folding soften steel, nickel, iron, or such metals (the exact metal is not clear because normally local call it by traditional name).



Some of the traditional practice to make the pattern more prominent, or making it lustre even more is to brush it with concoction of crushed realgar mixed with lime juice. I'm guessing it's some etching process going on. CRC handbook on metal etchant did mention realgar etching recipe. do you guys know how realgar might play part in this process? other candidate might be As2O3 instead of realgar or orpiment, arsenic sulfide.

another thing came to mind is that, in these sort of pattern work, wouldn't some more reactive metal in the mix act as sacrificial metal to the less reactive one? wouldn't it facilitate the rusting of the reactive layer?

Tuah Keris Pamor Sembur Emas.jpg - 309kB

Melgar - 24-3-2018 at 00:39

I know some stuff about this. The patterns have more to do with the crystalline structure of the steel than anything. And that alternates between ferrite, austenite, pearlite, and martensite, I think. Plus, working it changes the shape of the grains, sort of like how they make polarized filters.

Really, the main reasons they'd use that stuff is because that was more readily available than other acids like hydrochloric acid and phosphoric acid. But those are the acids I'd use, if your goal is to make the patterns more visible. They're still visible before "developing" the patterns with acid though, it's just that they're quite a bit fainter. But you'd definitely be able to see them at the right angle.

Sulaiman - 24-3-2018 at 01:12

The most valued Keris in S.E.Asia are those made from besi tahi bintang - meteorite metal.
(literally 'star-shit metal')
Lime juice is a common etchant and there is a lot of ritual processes involved in the manufacture.
..........
trivia:
My mother-in-law had such a keris that she always carried in her handbag,
even on international flights after 9/11 !
She said it is 'protected', and as I have accompanied her on international flights through all airport security - I'm inclined to believe her.
To-date I've not been able to take away the keris to examine it carefully as a distant brother-in-law now keeps it, along with a sword-type kris.
My wife's great-grandfather was a silat teacher from Indonesia, silat involves mysticism.
I wore a traditional Malay costume for our wedding - which includes a kris.


[Edited on 24-3-2018 by Sulaiman]

Vosoryx - 24-3-2018 at 20:03

AFAIK, (and this is my secondary hobby) the pattern is due to variations in the types of steel. In general, the less carbon, the lighter the shade of the etch. On edges where the carbon gets oxidized out of the metal, it's lighter.

I use a solution of FeCl3 to etch, though it is heavily diluted.

Interestingly, i'm actually editing a video on this subject for my youtube channel right now...

kuro96inlaila - 25-3-2018 at 20:57

Quote: Originally posted by Melgar  
I know some stuff about this. The patterns have more to do with the crystalline structure of the steel than anything. And that alternates between ferrite, austenite, pearlite, and martensite, I think. Plus, working it changes the shape of the grains, sort of like how they make polarized filters.

Really, the main reasons they'd use that stuff is because that was more readily available than other acids like hydrochloric acid and phosphoric acid. But those are the acids I'd use, if your goal is to make the patterns more visible. They're still visible before "developing" the patterns with acid though, it's just that they're quite a bit fainter. But you'd definitely be able to see them at the right angle.


ahhh I see so the pattern is a result of different crystal structure rather than drastically different composition being layered side by side.

yep the availability of classic traditional acidic substance is main reason they're use, other than being economically cheap. Since they do the job, local didn't really tried to replace it with stronger more effective substance like standard acid.
Quote: Originally posted by Sulaiman  
The most valued Keris in S.E.Asia are those made from besi tahi bintang - meteorite metal.
(literally 'star-shit metal')
Lime juice is a common etchant and there is a lot of ritual processes involved in the manufacture.
..........
trivia:
My mother-in-law had such a keris that she always carried in her handbag,
even on international flights after 9/11 !
She said it is 'protected', and as I have accompanied her on international flights through all airport security - I'm inclined to believe her.
To-date I've not been able to take away the keris to examine it carefully as a distant brother-in-law now keeps it, along with a sword-type kris.
My wife's great-grandfather was a silat teacher from Indonesia, silat involves mysticism.
I wore a traditional Malay costume for our wedding - which includes a kris.


[Edited on 24-3-2018 by Sulaiman]


yeah we do call meteorite "star poop" here hahahaa :D always a common thing to ask parents do star even poop like is it really a poop omg just imagine the childhood confusion.

ohh that's interesting, what occurrence make you inclined to believe her? they didn't detect the keris at airport or?
Quote: Originally posted by Vosoryx  
AFAIK, (and this is my secondary hobby) the pattern is due to variations in the types of steel. In general, the less carbon, the lighter the shade of the etch. On edges where the carbon gets oxidized out of the metal, it's lighter.

I use a solution of FeCl3 to etch, though it is heavily diluted.

Interestingly, i'm actually editing a video on this subject for my youtube channel right now...


Carbon get oxidized out of the metal, this happen during the weld phase or can it happen overtime on normal temperature? Seem like reverse-carburization at first hmmhmm

I wonder what mechanism it acts on for iron chloride to etch the metal. simple lewis acid I guess bc I remember reading iron chloride recipe can be used on non-iron metal. I could be wrong tho, my knowledge is really rusty bhahaha

I get the idea of using arsenic/arsenous acid for etching, but to use arsenic sulfide in form of realgar and orpiment doesn't seem to help the etching process theoretically. I mean, I cannot think of how they play the role here.

Fulmen - 25-3-2018 at 23:58

Quote: Originally posted by kuro96inlaila  
different crystal structure rather than drastically different composition

You can do both. Meteorites are often high in nickel, anywhere from 5-65% afaik.