copper alloys (brass, bronze)

Sat Oct 20 04:33:17 UTC 2007

I am forwarding this message to the list because Bill Ayres' posts bounce
back although he is a subscriber.

Paula Radetzky

---------- Forwarded message ----------
From: William Ayres <wsayres at uoregon.edu>
Date: Oct 20, 2007 12:29 PM
Subject: Fwd: Re: [An-lang] copper alloys (brass, bronze)

Date: Fri, 19 Oct 2007 12:42:12 +0800
To: David Mead <david_mead at sil.org>, an-lang at anu.edu.au
From: William Ayres <wsayres at uoregon.edu>
Subject: Re: [An-lang] copper alloys (brass, bronze)

As an archaeologist, I can offer some reponses to your questions.  I hope
these might be useful.

William Ayres

Your questions were:

1.  Given that we're talking about rural Indonesia, is there a "default"
expectation, e.g. would you expect a tray to be brass, or a gong to be
bronze?  How could I find out if my assumptions were indeed correct?

It would be difficult to make such a distinction based on just macroscopic
characteristics.  Many complex copper-alloy shapes that have been tooled or
machined (like a screw), as opposed to just cast, tend to be brass,
especially historic ones. This is because brass is somewhat stronger, but
you can't tell just by looking at the metal surface.  This would require
metallurgical analysis.  Today, while the distinction of bronze being alloys
of copper and tin (say 12% tin) and brass as alloys of copper and zinc (10%)
would be common in industry and many variants of the alloys exist,
prehistoric metal workers tended to produce copper alloys with combinations,
at low percentages, of several metals (primarily tin, but also lead,
arsenic, and perhaps zinc).  One technical definition of bronze is that it
contains no zinc.

Most archaeological *cast* specimens of the early copper alloys in Southeast
Asia are bronze, not brass, and the term "bronze" is widely used to group
all copper alloy artifacts (including those that contain some zinc) because
one can't tell what it is unless a metallurgical assay is performed.

2.  What were the centers for producing such metal objects, and how might
they have wended their way into, say, interior Sulawesi?

Coastal trade centers in Island Southeast Asia would be the main conduit of
metal goods coming into the islands early on, with mainland SE Asian mines
being the original source of the materials and some finished goods.  Local,
coastal re-working of copper alloy metals and metal goods probably began
soon after these were introduced.  The interior people acquired the metal
objects through trade.  As far as I know, no metalworking sites in the
island interior have been found, and small villages in the mountainous
interior would probably not have supported a metalworking specialist.

3.  Along with this, how old are such objects likely to be?

The earliest copper alloys--with tin, lead, arsenic, and perhaps some
zinc--in Southeast Asia (in the mainland) are approximately 2200-2000 BC.
They became widespread in the mainland by 1500 BC and considerably later
than that in the islands.

4.  Can you point me to any sources where I could learn more about
metallurgy in insular SE Asia?

Vince Piggot at the University of Pennslyvania Department of Anthropology is
well-known for his archaeological research on the origins of early copper
alloys in Southeast Asia.  You might look at Charles Higham's volume, The
Bronze Age of Southeast Asia, for a synthesis on the bronze age archaeology
of Southeast Asia.  Peter Bellwood's  Prehistory of the Indo-Malaysian
Archipelago (1997) is specifically on insular Southeast Asia.

William Ayres

At 09:34 PM 10/18/2007, David Mead wrote:

Hi,

When doing dictionary work on the island of Sulawesi, I've been befuddled
whether to describe certain metal objects as made of "brass" (copper+zinc
alloy) or of "bronze".(copper+tin alloy).  These metal objects include:

        axe heads
        bells
        gongs
        bowls (sometimes having a foot)
        trays
        box for betel-nut ingredients
        finger rings
        ear ornaments
        bracelets (both thin and thick)
        arm bands
        anklets (both thin and thick)
        thin rings worn above the calf
        head ornaments

My understanding is that it is difficult to tell the difference by simple
inspection. *Color*: brass with a high zinc content is yellowish, but
brasses with a lower zinc content can be the same color as some bronzes.

*Weight*: brass and bronze have very nearly the same specific gravity, one
is not appreciably heavier than the other

*Patina*: both brass and bronze develop a patina which can be rubbed off,
viz. become shiny in places where they are often rubbed..  Complicating the
picture is that "lesser grades of bronze can also have some zinc in the
alloy, resulting in properties closer to brass."

In a way, it's just a problem of the English language.  Malay uses *kuningan
*for "yellow brass" (brass with a high zinc content) but *tembaga *for
darker brasses as well as copper and bronze.  My understanding is that Dutch
*koper */ *koperen *also has about this same range of usage as Malay *tembaga
*-- though it would be good if someone could confirm this for me.

So my questions are:

1.  Given that we're talking about rural Indonesia, is there a "default"
expectation, e.g. would you expect a tray to be brass, or a gong to be
bronze?  How could I find out if my assumptions were indeed correct?

2.  What were the centers for producing such metal objects, and how might
they have wended their way into, say, interior Sulawesi?

3.  Along with this, how old are such objects likely to be?

4.  Can you point me to any sources where I could learn more about
metallurgy in insular SE Asia?

Thanks much,

David Mead

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