Giannis vs Polinik on the color of bronze :)

[Paullus Scipio]

Matt wrote:

I used to think the same thing, but Jeroen Zuiderwijk (another recognized expert bronze caster) has recently done some smelting.......Granted, there could be a big difference in ore types and quality, charcoal quality, furnace efficiency, etc. So where did we get those bigger numbers?

Most interesting, Matt - even given the differences you refer to, one would not expect a factor of ten difference in amount of fuel (Jeroen used roughly the same amounts of ore and fuel by weight 10kg of ore + 8 kg of charcoal to produce 3-4 kg of copper). Perhaps when attempting smelting on a larger scale, the efficiency drops......Also, it sounds like a very different grade of ore - far less pure - was referred to because 30 kg of sulfide ore only produced 1 kg of copper ( Jeroen got 4kg or so of copper from 10 kg of malachite) and that, I think, would account for a lot.....Jeroen evidently started with 'copper rich' ore (malachite, which is a corroded form of fairly pure copper).Notice that again a factor of roughly ten is involved..... It is quite possible both sets of figures are accurate in different circumstances, and notice that the very large quantities of fuel quoted apply "especially if the ore is dominantly sulfide".

John wrote:

I have always understood as others have said that the colour comes down to the exact alloy of copper used, and that zinc gives a more yellow brass-like colour compared to tin which gives a redder colour. I also have been given to believe that copper/zinc is something we find in the Italy and the west (Roman) while copper/tin is more Hellenistic and eastern.

....and Gregory wrote:

I have always understood as others have said that the colour comes down to the exact alloy of copper used, and that zinc gives a more yellow brass-like colour compared to tin which gives a redder colour. I also have been given to believe that copper/zinc is something we find in the Italy and the west (Roman) while copper/tin is more Hellenistic and eastern.

You'll notice I qualified my statements, and was using a generalisation - one would expect some variation depending on the type of ore used, and whether the bronze had a low (5%) or high(15%) tin content. The point I was trying to make was that by and large, ancient bronze looked more like brass than modern 'red' bronze......and it does !! The fact that there is colour variation e.g. from 'gold/yellow with a pink tinge' to 'gold/yellow with a brassy greenish tinge' or 'gold/yellow with a pale silvery/white tinge' does not negate this.....ancient bronzes, as many of the photos on this thread show, are hues of 'gold' not hues of 'red', or 'green' - unless a patina has been allowed to develop [digression: the presence of verdigris is a sure -fire pointer to a probable fake!] or 'grey'

Christian wrote:

Paul,
1. please look, e.g., at the metallurgical analysis of finds at Haltern or Kempten. What you say is not true.
You'll need to elaborate on which part you consider incorrect/'not true'. Phosphor bronze certainly didn't exist in ancient times. It is also true that ancient copper alloys were different to modern ones - so much so that metallurgical analysis allows easy detection of the many 'fakes' and 'pastiche' helmets foisted on collectors in the 19th and early 20th centuries. Even Brass is different - for example, Roman brass never exceeded 30% zinc content, while from the seventeenth century onward brass typically has a zinc content of 35% or more.
2. ancient bronze can not be distinguished from brass when there is a patina on it. That´s why the museums label "copper alloy", when there is no metallurgical analysis. Good publications try to find out the difference with metallurgical analysis (Haltern again, e.g.)
Agreed!....but it is also true that a typical bronze Greek or Roman helmet for example, with a tin content from 8-9% - such as is typical of a Corinthian - or 7-8% as is typical of a Montefortino, have a 'golden' appearance when new and polished that is all but indistinguishable from brass - the Munich helmet being a case in point, with not even a hint of 'pink' or 'red'.
3. removing patina does not necessarily show the original colour. When in ground or in water e.g. the tin may "move" towards the surface of the metal over time, resulting in a different colour on the surface than the one it originally had. Same can happen when heating a metal. If you want to see the original colour, you need to know the alloy and re-make it.
Also agreed!....It can be difficult to determine original colour without reproducing the particular alloy, because of changes over time....

The "yellow" helmet from munich / sicily looks in natural light like this:
Thanks for publishing these photos, which literally show the helmet in a different light ! :wink: Most interesting. However, even in those photos and despite the patina it is clear that the helmet is of a 'golden' or 'brassy' hue, not a 'reddish' or 'greenish' hue.....which is my whole point.

I don't think you will find us in disagreement here - I was merely enlarging and expanding on the points you made, Christian.
Dan wrote:

I have to agree. It is very easy to tell the difference between a copper-tin alloy and a copper-zinc alloy if they are new-cast and polished. There is more red in the tin alloy. It is a "warmer" colour. I tend to see a "greenish" hue in bass. As has been said, once they develop a patina and/or have been buried for a long time, you need metallurgical analysis to tell them apart.

Again, I don't disagree, it is possible to tell some 'bronzes', particularly modern ones ( and significantly, all the 'pinkish' hued examples here are modern reproductions), from brass with the naked eye, but in many/most instances ( and evidently depending on light conditions too!) ancient bronze artifacts had a 'golden hue' that was all but impossible to distinguish from ancient brass with the naked eye, and in general, ancient bronze was of a 'golden' colour very unlike the 'coppery/red' of modern bronze alloys, as can be seen from the photos posted in this thread, especially the Munich helmet ( and accompanying greaves, by the way) and the cast objects....... In simple terms, a layman looking at the Munich helmet/greaves, despite lighting conditions or changes wrought by time, would say it was made of 'brass' not 'bronze'.