Verifying A Metal (Gilding Metal?)

[Nigel Graham 2Participant @nigelgraham2]

Quite some years ago I bought what I thought was 3/16″ copper sheet, from a scrap-yard, intending to use it for my steam-wagon’s boiler… before deciding I would be better having it made.

It still had a label telling me what it is, and that is now illegible, but must have described it as “CZ121” as I wrote that on the metal with a felt-tip pen.

I was told this is “Gilding Metal” – a type of brass but with a very low zinc proportion, though still not advisable for boiler-making. It has oxidised to a dull copper colour, but is still a bit brighter and redder than pure copper turns. However, that grade made be either wrong or superseded.

I started using a piece of it today, by sawing, drilling (step-drill and twist-drill) and milling, and although the cut surface and chips have a slightly brassy appearance and it does not seem as “sticky” as copper, I am not sure now quite what it is!

Does anyone know a way of identifying this stuff as either commercially-pure copper or a low-Zn brass easily, please, bearing in mind I do not have a metallurgy laboratory at my disposal? Would for example, comparing heating & pickling colours of samples help?

 

[DiogenesParticipant @diogenes]

CZ121 is free-machining leaded brass – often the supplied grade for drawn sections from most ‘hobby’ suppliers..

Still current and easy to find data on the ‘net..

Edit – it’ll contain a lot of zinc

[JasonBModerator @jasonb]

CZ101 is gilding metal

[Nigel Graham 2Participant @nigelgraham2]

Thankyou.

I followed that by examining suppliers’ publicity and discovered that firstly the brass is not sold as sheet, only various forms of bar, and secondly it looks much more like brass than this stuff I have.

The grade for gilding-metal I found seems to be CW, as well, but I don’t know if this is a more modern designation. I probably bought the metal a good twenty years ago, and it had a stick-on label giving stock-control information including specification..

 

I have just paused to go and look, and yes, CZ121 is what I had written on the sheet, so that seems wrong. Possibly the label was already damaged. So perhaps I have identified it correctly as “gilding metal” but quoted the wrong specification from the label, which is now too faded to read at least in artificial light.

At least the CZ does show this is some form of brass.

 

My question about the reaction to pickling goes back to when I once sectioned a worn-out injector, polished the exposed surface with emery then lightly pickled it. I can’t remember with what acid, but the cones and body did emerge with slightly different hues.

So I could try with this material is cleaning, polishing and pickling in the same acid in different pots, an off-cut of each of this suspect metal, copper water-pipe, brass and perhaps, phosphor bronze and compare the results. It will not identify the real nature of the metal if it is an alloy, but may show if it is or is not pure copper.

 

[DiogenesParticipant @diogenes]

CZ121 is / was available as sheet..

Whatever the grade it doesn’t sound likely likely to be copper, do I detect a certain amount of wishful thinking..?

Are you looking for material for a boiler?

[JasonBModerator @jasonb]

Yes CZ121 sheet is available here

So if you have read the label wrong how far out are you, copper could be C101, but if it is a golden colour rather than copper and bends easily likely to be guilding metal.

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