Would you care to opine on why craftsman of old chose brass or bronze as their alloy of choice?

I have moved this topic to the off topic forum from the Historic Arms Talk forum. Please note that the Historic Arms Talk forum is described as "Discussions of reproduction and authentic historical arms and armour from various cultures and time periods". The off-topic forum is a catch-all for other topics of interest to this site's audience that are not specifically conversations regarding arms nor armour.

This topic is about alloys and not about a specific arms or armour item and so is best put in the off-topic forum.

Thank you.

Well, a lot depends on how far back you want to go! In the Bronze Age, zinc or zinc-containing compounds were apparently just not known, so tin was the way to go, hence bronze. The Romans seem to have started using brass (orichalcum) in the late first century BC. Interestingly, it was apparently only used for coinage and military equipment, so it's as if there was some sort of government monopoly on its use. Civilian or domestic stuff, including cookpots used by the army, continued to be made of bronze.

"Why?" As usual, that's a perilous question, unless the ancients actually write something about it. We could speculate ad nauseum about hardness and ease of working, or cheapness, or whatever, but the way the alloys varied, all of the properties and costs would vary, too. Of course there were alloys that had both zinc and tin, which in Roman stuff is often seen as a result of recycling. In other words, there was no real reason for them to add tin to a brass alloy for a particular buckle or other item, since most of the other items of that type didn't have any. When mixing up a new batch of metal, they were certainly capable of getting the alloy they wanted, but naturally recycling is more of a crap shoot.

In short, the ancients did a lot of things for reasons that we haven't figured out yet, and they all too often did them consistently or at least repeatedly. I tend to just say, "Why not?", and leave it at that, to avoid too much dangerous speculation!

Vale,

Matthew

Most metallurgists think that terms such as "brass" and "bronze" are irrelevant since many alloying elements exist in most historical artefacts. Better off simply using the term "copper alloy" and then specifying the primary alloying elements involved.

What do you mean by "alloy of choice"? This would indicate there were other suitable or equal alternatives, which there weren't. During its heyday bronze was the metal of choice becuase it was the state of the art in metalurgy at the time. That's why it was chosen. When other superior alternatives were developed bronze was replaced in its role as a material for warfare. It wasn't as if they had a shopping list of alternative metals to choose from that were equal in thier properties.

I'm fairly sure you can make a good blade with bronze but I doubt that you can get good results with brass ?

Maybe they both can be work hardened but I've never heard of a brass razor but bronze could be sharpened enough to shave.

Many different formulas for bronze, some only modern alloy, but for cutting weapons or tools not all bronze alloys would
be useable. ( Optimum ? )

For other things brass or bronze might each have some advantages / disadvantages ?

I think that it might be because brass doesn't hold an edge very well, but I have no idea about the edge retention of bronze or how it compares to brass...

Interesting topic :)

I read on another site that zinc wasn't even a known element in ancient times, but often was found with copper for ready made brass in some deposits. India I believe was sort of "blessed" with a lot of copper/zinc deposits whereas Europe wasn't so much.

Tin was mostly found in Cornwall in Britain and traded a lot from there. So Bronze was pretty limited in its production compared to Iron or Copper.

I suppose you can find an atlas or Encyclopedia and find out more. I plan to do some research on this subject this weekend when I have time. ;-)

I've never heard of brass being used for blades, since it didn't come into use until well after decent steels were already well known. But the Romans were making brass, bronze, and iron helmets side-by-side for several centuries, so presumably they felt the protective qualities were similar enough not to matter.

Arsenic was one of the first things alloyed with copper to make it harder, but tin was better in many ways so tin bronzes took over very quickly. Oddly enough, it doesn't seem like straight copper was used much during the Bronze Age or later, probably since adding a little tin made it so much more useful and easy to work with.

Valete,

Matthew

I've been playing around with copper alloys and ancient techniques connected to them, so I try to answer this one.

Different elements affect the properties of the metal drastically. In copper alloys the most usual ingredients have been tin, zinc and lead. Depending on what kind of material the craftsman had available and what properties he/she wanted, some or all of them would have been present in the used alloy in differing quantities. In my opinion the most important characteristics of the metal for the craftsman would have been:

-Hardness / toughness
-Appearance (colour, shining)
-Castability
-Coldworking properties (Hammering, turning, filing)

When impurities are added to copper they always lower the melting point of copper, which otherwise would be hard to achieve on a charcoal fire of a moderate size. This is the reason why they are always present on cast objects. Basically the more they added tin, lead or brass (zinc+copper) in to the crucible a) the easier it was to reach the casting temperature b) the better the molten metal would flow in to the mold.

In viking age Finland for example the cast copper-alloy jewelry has often a high lead content up to 40%. Sometimes the alloy has more zinc than lead but usually both. Tin bronzes seem to be pretty rare .

In medieval London all of these alloying elements appear, sometimes together in all sorts of ways. Sometimes there are parts made of different alloys soldered in to the same piece.

We have documents from the Roman times for different "recipes" for bronze. They used certain alloys for certain purposes, this can be seen in the studied artifacts as well as written records.

I'll go over the qualities of tin bronzes since i'm more familiar with this material.

pure copper is a red metal. It's very soft and easy to hammer cold but hard to cast.

When we start adding tin the metal becomes harder, the melting point lowers and we get better castability. The color gets to the familiar "brown" bronze color and as tin content rises the color gets lighter.

If we want to draw wire or work the metal a lot when cold (In to a sheet for example) we are usually talking of a bronze with less than 10% tin.

10% tin is the classical cast bronze, ideal for bronze tools. It can still be worked cold and work hardens to a cutting edge. It is tough enough yet hard enough.

After about 13% the bronze gets too hard and brittle to really hammer or bend but the casting properties get better.

20% tin is the classic bronze for bells. It is hard and so has a clear 'ring' to it. It still has some of that bronze color. Theophilus gives the 1/5 tin ratio for bell bronze in 'The divers Arts' from 11th century and if you buy bell bronze today you still get the same stuff, at least here in Finland.

When we go up to 25% tin we have a white metal as hard as glass. When polished I think it looks as if chromed. There's a button from 14th century London of a white tin bronze.

Zinc affects the alloy in many ways resembling tin. You just need more zinc to get the same effect and the color starts out as yellow. The patina on brass is like stained, I think thats one of the reasons why bronze is seen as "more valuable" today though the price difference isn't that big.

Lead is a very powerful element when lowering the casting temperature. It makes the color duller and is no good if you want to work the object with a hammer, but it makes filing easier(I think).

I don't know if this clarified the issue in the least. :)