Copper, bronze and brass. How to treat them.

[Modeler12]

We are all working with one or more of the copper alloys. Perhaps it is good to know some of their characteristics. Here is a good web site http://www.diffen.com/difference/Brass_vs_Bronze

 

But how does that effect us, model ship builders? 
To make strops, hooks and other parts that require delicate bending it would be nice to have a wire that is malleable.
Copper is, but it also is soft and prone to corrosion. 
Brass is also, and used a lot for just that purpose.

Bronze is the 'unknown' for most of us. It falls between brass and copper in composition but may have some neat usages for us.

 

Somehow I inherited this spool of 26 gauge bronze (at least it looks like that compared with brass and copper). It is ancient but I have used it a few times. It is harder to bend than brass, but for me it gives a sturdy, beefier 'hook'. It takes a bit more care but you might try it if you can find it. Too bad I don't have a spool in a thinner gauge.

 

 

It took a piece of each and experimented with the 'Patina' that I described earlier for blackening metals. 

Below are the results.

 

The brass wire, bought at a craft shop, did not do well because it has this protective coating. However, after I rubbed that with some steel wool it came out just as well as all the others.

[mtaylor]

Jay,

Try annealing the bronze by heating to red hot and letting it cool.  Works a treat to make brass workable.

[Modeler12]

Indeed, Mark, and you don't need a torch to do that. A simple candle flame will work.

[wefalck]

Bronze is the 'unknown' for most of us. It falls between brass and copper in composition ...

 

Well, not exactly. Brass is an alloy of copper and zinc, while bronze is an allow of copper and tin. While brass usually only contains Cu and Zn in varying ratios (tombak is a high-Cu brass), bronze may have additional components, such as silicium (Si), aluminium (Al) or mangan (Mn) to enhance its corrosion resistance or its properties as bearing metal. In general, bronze typically is more corrosion resistant than brass, which is why it is used e.g. for propellers. 

 

Hardening or annealing brass is just the reverse of that for steel: quenching it after heating will soften it, while letting it cool down slowly will harden it. Particularly bronze can be hardened by hammering  (see bronze age weapons) or pressing it (the Austrians used hardened bronze for their guns, while everyone else switched to steel).

 

wefalck

[molasses]

The link in the first post is bare bones basic. There are literally many thousands of copper alloys, each designed for specific purposes.

 

The brass sold for hobby use is a 75/25 copper/zinc alloy and it is in the half-hard condition. The brass in firearm cartridge cases is 70/30. Most copper alloys work harden which greatly increases the strength but also makes them more brittle. For example, if you draw annealed (also called "soft" or "dead soft") brass wire through a draw plate you'll have to anneal it after two draws. One draw will render it half-hard. It won't draw a third time, it will usually just break and if not will be so brittle it will break if bent.

 

Annealing of most copper alloys is done as described by wefalk: heat it until it glows then immediately quench in water. The result of heating until it glows and letting it air cool is very unpredictable. If brass is heated to about 800 F and quenched it will partially anneal to about half-hard.

 

Navy brass is an alloy of copper, zinc and tin which retains the brass color while also having the higher corrosion resistance of bronze. This is the brass alloy that was used on ships. Muntz metal is a 60/40 copper/zinc alloy with a trace of iron that was frequently used for hull sheathing at a much lower cost than copper after its invention in 1832. See the Cutty Sark website for an example of its use. It looks very similar to brass but a bit whiter.

 

True bronze contains 8% to 12% tin. Architectural and commercial bronzes are actually brass, with zinc instead of tin, and sometimes also contain lead. That's why modern "bronze" statues turn green while some of the older statues that were cast in true bronze remain the same deep reddish brown they were when cast 200 years ago.

 

Copper is also alloyed with nickel for high corrosion resistance, especially in seawater; the most widely used for this purpose - Monel - is 45% copper, 55% nickel. Another copper nickel alloy (usually with some zinc) known as German silver contains no silver, but closely resembles it. If you ever had a "silver" ring that turned your finger green it was made of German silver. Nickel silver is a standardized alloy of copper/nickel/zinc (60/20/20, again no silver) used (among many other things) for the rails in model railroading because the oxide that it forms is also white, protects the metal against further oxidation and conducts electricity. It is also used to make most professorial grade white metal musical instruments as opposed to the lower quality yellow brass instruments.

 

Sorry if I've presented more info than you want or need to know but I spent my entire adult life working with metal and am still fascinated and amazed by what can be done with it.

[Modeler12]

Well, I beg your pardon guys if I over simplified. But like I said there are many non technical members on this forum and some may not realize that brass and bronze are not the same thing. For our purposes of modeling ships, bronze is not used very often, but it just so happened that I came across some bronze wire.

I just did not want to go into all those details that a metallurgist would drool over.

[molasses]

Well, I beg your pardon guys if I over simplified. But like I said there are many non technical members on this forum and some may not realize that brass and bronze are not the same thing. For our purposes of modeling ships, bronze is not used very often, but it just so happened that I came across some bronze wire.

I just did not want to go into all those details that a metallurgist would drool over.

 

 

I certainly did not intend to cause any offense. I apologize for inadvertently doing so. It was worthwhile for you to post the link to that basic information and the results of the chemical coloring of those different wires.

 

My intent was to correct the statement that bronze "falls between brass and copper in composition" without stepping on anyone's toes, and to expand a little with examples of where copper alloys were used historically on sailing ships as well as in a few items with which most people are familiar. I also wanted to explain how common brass work hardens and how to anneal it.

 

I believe that presenting more information, simply as background to provide a more complete picture of the subject, is better than less - and infinitely better than a statement presented as fact that is undeniably false.

 

I again apologize for causing offense.

 

Dave

 

P.S.  As a follow-up to your tests, I have some white metal craft wire that I suspect is either solid copper-nickel or copper-nickel plated copper wire. I know it isn't silver or silver plated because the packaging didn't say so and the price didn't reflect it. It doesn't blacken with a selenious acid based product, probably because of the nickel.

[Modeler12]

No problem, Dave and no apology is necessary, please. You were right and I was in error by simply saying that bronze is somewhere between copper and brass. 

 

Since you are an expert on metals, can you tell me if the spool of wire I showed above could be bronze? Is there a simple test for that. I suspected that it was not brass because it is too orangy in color. I tested it with the selenium acid solution and it worked fine. Probably because of the copper content. 

 

I also was interested in your comment about the nickel in model railroad track. I was curious about the difference and pulled out a couple pieces of track that have been in my attic for a couple decades. One small piece was from the old brass track and the other from the nickel alloyed material. The brass was badly oxidized and the other had a greyish cast. I sanded part of the track and coated one section with the selenium 'patina'. The brass turned black very quickly but the other one took a long time to finally show the black oxide coating.

So, I am not so sure that a little nickel in these materials will prevent the blackening. Although stainless steel tongs (which also contain nickel if I am not mistaken) will not be affected. Low carbon steel will blacken. 

Figure that one out, Dave.

[molasses]

Thank you Jay. I would not call myself an expert, I'm a retired welder and occasional machinist who learned something about metals from working with them. My later few years in the industry were in QA/QC (welding inspection).

 

Based upon your description of the wire in question it does appear that it is some type of basic bronze as you said. I can't think of any inexpensive tests that would tell what it is. As you mentioned, it is stiff and makes good hooks.

 

I didn't test my presumed copper nickle wire for very long. It could also be nickel plated.

 

Stainless steels have chromium (above about 10%) which provides most of the corrosion resistance.

 

On the rails the grayish cast is the oxide coating which conducts electricity as I said in the other post. The oxide on the brass does not which gave model railroaders fits and required constant maintenance until someone hit on using copper nickel rails without increasing the cost significantly. Some model railroaders objected to yellow rails (the fanatics  ) even after painting them and sanding through the paint on the top of the rails. Painting the rails, removing the paint from the top and leaving the oxide coating on the copper nickel rails was considered more realistic. I was interested in model trains for a while but I found I got bored very quickly running the trains, but I enjoyed the modeling aspect very much, so I went back to building ship models.

[wefalck]

The classical surgical/laboratory stainless still is 18/8, which means 18% Cr and 8% Ni. The variant of steel alloys is legion and there are many more alloying metals in use, such as manganese (Cr-Mn-steels are in addition to Cr-Ni-steels used make armour plates for ships).

 

There are also Ni-Cr-alloys without iron, which are used e.g. as resistance wires and in electrical heaters. The wellknown miniaturist modeller Lloyd McCaffery swears by them for making standing rigging - they don't corrode and don't sag like copper.

 

The oxidation behaviour of copper alloys is quite complex and depends on the environmental conditions and the history of the oxidation process. So the effect of blackening agents is difficult to predict. However, the trades supporting sculptors working in bronze do know very well how to control the process of patination and there are textbooks and recipies available (also in the Internet).

 

Nickel silver (also called German Silver, Alpaka, Argentan, Maillechort) is an interesting material (60% Cu, 20% Ni, 20% Zn) that has similar machining properties to brass. Unfortunately for us modellers, it is not available in the same variety of shapes and sizes as brass. It would be very useful for parts that have to stay silvery. Otherwise it is used in large quantities industrally, mainly as the base metal for silver-plated cutlery. Because it tends to be harder than brass, very thin photoetched parts are often made from nickel silver rather than brass.

 

wefalck 

[ianmajor]

I am a great fan of using nickel silver, in fact I am making a Brodie stove from it at the moment. It is a nice material to work with which as Wefalck says can be left in its bare silvery colour.

 

I find I have no problem with using blackening products on it.

 

Two advantages it has over brass.

 

1) Paint keys in to its surface better than brass. Even with etching primers paint peels off brass long before it does on nickel silver particularly around sharp edges.

 

2) I find nickel silver conducts heat less well than brass which means that when soldering detail in place the heat spreads less quickly to adjacent detail making it less likely to fall off.

 

One point against nickel silver is that it is more expensive which probably explains why it is not readily available in shapes other then bar, sheet or rod.

 

BTW on my avatar, between my hands, is a model that is being made from NS. 

 

Ian M.

Edited May 19, 2013 by ianmajor

[druxey]

Thank you, gentlemen, for this interesting and informative discussion!

[patpdm]

All of these can be easly blackned by dipping them in gun bluing not sure how it may effect the solder joint though.

[zygote01]

Could someone out there please give me some assistance regarding the straightening of brass moulded strips? I have a Panart San Filipe (more fool me) that has long brass mouldings that have been bent into 'horseshoe' shapes to get them into the box. Why, I do not know as the box is big enough for these strips to be supplied as straight lengths.  I have tried annealing them whilst dangling them with a heavy weight at one end. It helps a bit but they are no good enough for use. Please bear in mind that I do not have access to a machine shop. Thanks in advance.

[wefalck]

Actually, this thread was about surface treatment of the said materials … perhaps you better make up a new thread on your subject.

 

Anyway, what is the size and shape of these mouldings ? With this knowledge one could perhaps make some suggestions.

 

When annealing brass, one need to remember that it behaves the opposite way of steel: if left to cool slowly, it hardens. So one needs to cool it down quickly.

 

wefalck