Author Topic: Telling the difference between brass and aluminium-bronze  (Read 5122 times)

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Offline FosseWay

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Re: Telling the difference between brass and aluminium-bronze
« Reply #15 on: July 14, 2016, 11:01:09 PM »
  This coin is aluminum bronze.     

Do you mean one of the coins/tokens illustrated upthread, or did you mean to attach a picture?

Offline bgriff99

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Re: Telling the difference between brass and aluminium-bronze
« Reply #16 on: July 15, 2016, 08:28:27 PM »
The one you posted is aluminum bronze, if the alternative is normal coining brass.  All sorts of mixtures were used for tokens, but presumably in wartime, not nickel, which makes copper pale at low levels.   Extra zinc makes the metal too hard to strike.   Lead softens it.   Manganese was not a wartime necessity, and up to 3% improved ductility.   Tin would not be used.   It was even possible to add iron.   Without knowing the brass composition, or at least having other coins to compare, it's speculative.   But your coin is not cartridge brass or any binary mixture at 30% or less zinc.

Offline FosseWay

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Re: Telling the difference between brass and aluminium-bronze
« Reply #17 on: July 16, 2016, 09:46:14 AM »
That is very useful to know, thank you. Now to learn to spot the difference...

Have you got two coins, not necessarily identical in design but of equivalent wear, made of al-br and brass that you can post side by side?

Offline malj1

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Re: Telling the difference between brass and aluminium-bronze
« Reply #18 on: July 16, 2016, 01:13:19 PM »
Both the $1 and $2 Australian coins are Aluminium bronze =

Composition: 92% Copper – 6% Aluminium – 2% Nickel

Malcolm
Have a look at  my tokens and my banknotes.

Offline bgriff99

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Re: Telling the difference between brass and aluminium-bronze
« Reply #19 on: July 16, 2016, 03:23:12 PM »
I said the token you posted was aluminum-bronze based on its color, but it appears to have more aluminum than the French 1 and 2 franc series.   If both kinds of tokens appear the same, then the alloys of later issues probably were adjusted to match.   There are too many unknown variables here.

I have French 1 and 2 francs by date, untouched for 25 years.   The aluminum-bronze ones have slightly reddened, and are indistinguishable from brass.   Here is a comparison, at similar luster, of the aluminum-bronze type, and a US-struck one literally of cartridge brass.  In hand the 1940 piece actually looks more like brass.   In the scan perhaps a tiny bit more yellow saturation can be seen in the 1944 coin.

If the zinc level is increased from 30% to 35% or more, brass is equally or less yellow than the French coins.   I say that based on late 19th century struck brass cash.   At any combination of luster, wear, and oxidation, they are indistinguishable from the French coins.

So I retract my statement that aluminum-bronze can be spotted by color.   Does anybody know the exact composition of the French coins?    Aluminum dissolves into copper up to 10%, without forming a compound.   I don't have information about elongation, tensile strength, hardness for the varying levels.   

Offline bgriff99

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Re: Telling the difference between brass and aluminium-bronze
« Reply #20 on: July 16, 2016, 04:02:44 PM »
Presumably these are of identical composition.   The 1921 piece has the paler color associated with lustrous aluminum-bronze.   The 1923 has begun to redden, which gives it a more yellow color.   Scanning makes colors look different than viewing at a single light angle in hand.   The 1923 actually looks quite red, like brass at 20%-25% zinc.   Aluminum bronze seems to be able to take on a wide variety of hues depending on how lustrous, how oxidized, and how recently and vigorously circulated. 

Offline Gusev

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Re: Telling the difference between brass and aluminium-bronze
« Reply #21 on: July 16, 2016, 04:23:12 PM »
Yes, the color can not be taken as a criterion.
Depending on storage conditions, the color varies greatly.
For example:
Nepal 4 paise 1955.
Metal - brass cartridge.
"Those at the top of the mountain didn't fall there."- Marcus Washling.