Mike,

There are lots of proviso's but as machined brass is likely to compare to the colour of a battery hen's egg yolk, a paleish yellow. Depends on which bronze you look at but phoshor bronze would be more like a duck egg yolk, a slight reddish tinge to it whilst manganese bronze would tend to look more silvery. Give them a week or two in the air and they all would start to change colour through forming an oxidation layer.
If you are actually there at the machining stage each material displays different cutting characteristics
Brass bars cut freely and sometimes have been known to sing to you. Phosphor bronze is tougher but still cuts very cleanly as you would expect from a bearing material. Manganese bronze and several other alloys of bronze are quite tough to machine and can work harden whilst cutting.
Bob D

I think the best way is to measure the density: weight the piece, put it in a graduated bowl half filled with water to know the volume, divide the weight by the volume, compare the result with the one for a brass sample. Brass density is lower than bronze one as brass is usually copper with about 40% zinc while bronze is copper with about 10% tin, zinc and tin having almost the same density.
J Maurel

John, Thanks for the info; for my needs all I have to remember is PB1 and Colphos. Steve

Hi, machining it will give you a good idea. Phosphor bronze, as sold for plain bearing bushes etc, comes off the tool bit in long strings. Brass and gunmetal produces fine chips. Gunmetal stock bar seems to be cast so it has the sand cast look, brass is extruded so smooth, clean finish. I notice gunmetal machines the easiest and is very soft. I often post questions on how to ID it as well as I have a shed corner full of boxes of offcuts of bar and sheet. You do get to tell what's what after a while, clean off some known samples with ajax as a reference and compare. Aluminium bronze castings for dome covers are being produced but the finished polished look is a bit too silvery for my personal preference.

A year ago, I spent some time researching bronze composition when I found there was little written about the subject. At the risk of criticism for errors I offer the table below. I gathered the information by searching the web for many worldwide manufacturers/suppliers, and came up with this. Please note that some suppliers may vary the composition by several percentage points, and there is potential for the use of added nickel in some bronzes.

The true phosphor bronzes are PB1 and PB102; although Colphos 90 contains phosphorous the addition of lead and zinc makes it quite different from PB102. People call bearing bronzes phosphor bronze, which I think is wrong.

For beginners in bronze I would stress the use of PB102 for anything attached to a steam boiler. There is a thought that the zinc in other bronzes could be leached out (as with brass) leading to a weakness, but I have not read of any proof of this. It was this issue that caused me to look at the compositions when I realised that some of our suppliers were not fully clued up on the subject.

Having said the above about suitability with steam, I presume that bronze castings are a simple gun metal and its use in cylinder castings works without problems. Colphos 90 and SAE 660 are regarded as bearing bronzes and you can see that their composition is similar. I understand that the aluminium bronzes are potentially hard, have come about from aerospace technology and are probably best avoided by us.

LG2, PB102, SAE660 and Colphos 90 are commonly available. PB102 machines ok and silver solders nicely, but it can be fussy about drilling and is difficult to ream. Colphos 90 and SAE 660 will also silver solder well and are that bit easier (softer) when machining.

Norm.

My father in law who worked as metallurgist in 13 year in Dnepr motorcycle factory in Kyiv. He told the bronze bearings in the motorcycle was made of 200 gram copper and 15 gram tin. First melt the copper then soak the bit of tin into the molten copper to prevent the tin is evaporated away from copper and stirr well before poring.