Brass Bowl

The alloy appears to be copper based with high iron content.
Any idea of the origin and the purpose of the piece?
The small round depression at the center of the interior, does it mean that the bowl was machine worked? If so, I guess it could not be very old?
Thanks

 

Can someone confirm if the hole is from the piece being turned on a lathe?

 

If the hole is conical it is almost certainly a lathe center. The machinist uses a special very short drill bit to drill the center hole, which leaves a hollow cone with the same angle as the lathe center's point. The center is exchanged for the drill in the tailstock, the "workpiece" is fastened to the motorized spindle with a chuck or faceplate, and cutting, polishing etc begins. The center is a hardened steel point with an included angle of 60 degrees, to which grease is applied to allow it to serve as a small bearing.

 

I guess the hole can be called conical.
Turned on lathe at some point? Like at what point? I guess shortly after it was cast? Hope I am not wrong again when I say cast. But how exactly was it done? The initial form was plain bowl and then it was turned on the lathe to work its current shape?
I guess they did not have some kind of mechanical lathes for working metal back in a days, so it could not be antique.
In this case I feel like I cleaning the verdigris. What should I soak it in?

 

Spinning metal goes back thousands of years.

 

I should have educated myself first. I just read that indeed metal spinning goes waay back.

 

Just remember spinning is different from turning on a lathe. A lathe is normally used for removing metal from an object by cutting down the outside or boring out the inside.

Spinning as in the video is shaping a disc or other shape metal piece into a different shape, for example making a 3D object from a 2D object. In the video they are using a special spinning machine, not a lathe, and the metal is pushed, not cut except for trimming.

 

How did they figure this Tang bronze bowl was spun but not cast?
http://www.trocadero.com/stores/brianpage/items/1304434/item1304434.html

 

I don't know really, maybe it was just assumed that was the easiest way to make it. I do wonder how they powered their machine to get high RPM back in year 700. Maybe 200 squirrel cages linked together? The ad refs a book you can get for $5, maybe buy it and find out. http://www.amazon.com/Korean-Art-Brooklyn-Museum-Collection/dp/0876635168

We joined Amazon Prime and get free shipping so I've bought a number of books lately.

The ad you linked says the Koreans started with a bronze cylinder which was then spun into a bowl. How'd they know that? How'd they make the cylinder? Casting? I wonder if they didn't mean brass when it talks about spinning malleable metal because bronze isn't malleable. I'm sure the guy selling the bowl wouldn't want me as a customer, I ask too many questions.

 

They didn't figure, they made pure fiction in order to sell their trash

You really need to learn to differentiate poor condition from age at arms length

Your bowl is a poor condition piece of modern junque from India

Carry a decent magnet. India brass is almost always slightly magnetic. I have not run across magnetic brass from anywhere else. Brass or bronze should not be magnetic at all.

 

It is quite possible that what I have is recently made in India piece. But what's with words like "trash" and "junk"?

Mine bowl attracts slightly to neodymium magnet. So, most likely the copper is mixed with some or all of these - nickel, iron, manganese, cobalt ... together with zinc probably. I doubt it is copper plated iron.

It is somewhat true that a lot of copper alloys from India are slightly magnetic. But not all of them. And not sure if only pieces from India have that characteristic.

Also, Ancient bronzes were not always alloys of just cooper and tin. Here you can see that other elements were mixed as well:
http://www.jstor.org/stable/pdf/660717.pdf?acceptTC=true
Plus, a lot of the copper was smelted ore rather than native copper so impurities of other elements were present.

A bit of off topic, electromagnetic filed can be created between non-ferrous metals and neodymium magnet.


Now, back to the trocadero bowl.
I am not sure how they figured it was Tang Dynasty. Also, spun bronze is very unlikely, so they should have used the term "copper alloy" instead.
The comparison with the Korean spun bronze is not backed up by anything. Here is the extract from the "Korean Art from The Brooklyn Museum, by Robert J. Moes"



There is only one example of what they called "spun bronze" - a wine bottle from Koryo Dynasty, 13th century. Again, this is most likely not bronze but brass or other copper alloy. If not wrong, this is the same bottle
https://www.pinterest.com/pin/484559241132832514/
I wish the author cited the source describing the spinning technique.
Something that I don't understand. The bottle was made out of four parts, brazed together ( 3 spun sections and the upper one cast). How did they spin those sections? They are open from both sides, how do you turn them on lathe?

The earliest illustration of a lathe is from a well known Egyptian wall relief carved in stone in the tomb of Petosiris dated some 300 BC.
http://www.turningtools.co.uk/history2/history-turning2.html
http://www.stuartking.co.uk/index.php/history-of-the-lathe-part-one-reciprocal-motion/

Most likely metal spinning existed in Ancient times but I am just not finding any examples and detailed information on the subject.

A good read on ancient metal casting in China. Nothing mentioned about spinning.
http://www.foundryworld.com/uploadfile/201131449329893.pdf


Still investigating

 

Probably unimportant but the two photos of metal wine bottles are either of two different bottles or each photo is of a different side of same bottle with differences between the two sides. The latter possibility is of course much less likely than the former.

 

Two Zhou Dynasty (1046-256 BCE) bowls, possibly spun on lathe.





https://translate.google.com/transl...blog/s/blog_53de3f9a0100fuzd.html&prev=search

A Tang bowl. Not sure but looks like it could have been spun


https://translate.google.com/transl...rtron.net/thread-2930938-1-1.html&prev=search

 

Those both look like bronze which isn't spinable as it isn't malleable. Even if we assume they are made of some malleable metal, you can't spin-fabricate an object with protrusions like those opposed handles attached. The handles look like they were cast integrally with the bodies of the pieces. If they were made by spinning, the handles would have had to have been attached somehow after the spinning was all done. Also, one of them where you can see the wall thickness is too thick to have been made by spinning.