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Techniques for CollectorsCopper alloys

11th Jan 2018 19:28 UTCMatt Courville

I was wondering by chance if anyone out there knew what alloy of copper results in a red-copper coloration. I've attached a photo below with some alloys but have been unable to find a metal based link to the red color.

Thanks so much

11th Jan 2018 20:35 UTCKen Doxsee

This might help:

American Foundry Society

Look about half way down the page, under the heading 'Brasses.'

Ken

11th Jan 2018 20:45 UTCRalph S Bottrill 🌟 Manager

I would think the red colour is proportional to purity of the copper? Plus some oxidation to cuprite.

11th Jan 2018 20:47 UTCTed Hadley

It is alloy 110 copper: Pure oxygen free copper.

11th Jan 2018 21:01 UTCKen Doxsee

Info from the page I linked:

Red Brass (C83300 to 83810)—The red brasses are alloys of zinc (1-12%) and tin (0.2-6.5%) and may contain lead (0.5-7%). In red brass, lead is present to promote pressure tightness in service and to facilitate free machining during manufacturing. The red color is due to low zinc content. The highest volume red brass alloy (C83600) has been used commercially for hundreds of years and accounts for more tonnage than any other alloy.

Semi-Red Brass (C84200 to C84800)—Semi-red brass has higher zinc content than the red brasses, which reduces corrosion resistance, lowers raw material costs and lightens the color (but has little effect on strength). Because of their outstanding aqueous corrosion resistance, red brass and semi-red brass often are used in plumbing fittings, such as unions, valves and water meters.

11th Jan 2018 21:48 UTCHoward Heitner

Any brass used in plumbing fixtures in the U.S. has to be certified as lead free.

11th Jan 2018 22:49 UTCPavel Kartashov Manager

Dear Matt,

you never distinguish bronzes from your table each from other and from pure copper by eye (by color). All they are copper red. May be only Be bronzes, which are more light in color.

Note also, that yellow brass (Cu₃Zn) may to be covered by 100 mkm layer of pure copper for better corrosion resistance.

11th Jan 2018 23:55 UTCMatt Courville

Thanks for the info/links. The red looking copper on the left side in the photo was so visually different, I though to ask for another unrelated topic. Ted does the oxygen free copper occur in nature or is it only synthetically made?

12th Jan 2018 02:08 UTCTed Hadley

>Ted does the oxygen free copper occur in nature or is it only synthetically made?

I do not know for sure but I would say so. However, I have been told Keewenaw MI copper is close to oxygen free. One way to tell is oxygen free is more ductile and gummy, and tends to crack less when mechanically worked. Probably oxygenated copper has minute cuprite inclusions which interfere with ductility.

12th Jan 2018 04:08 UTCAlfredo Petrov Manager

I have some copper to which 0.5% Te was added to produce the opposite effect: eliminate ductility. That gets to be important when you want to turn copper on a lathe. (I don't see that listed on the copper alloy table above.)

12th Jan 2018 17:00 UTCTed Hadley

Indeed Alfredo is correct.

However, looking at the shapes of the items in the photo, one can see most are drawn or stamped, so high ductility is necessary, which implies alloy 110, which is probably the most commonly used alloy of copper (most all copper pipe and fittings, copper wire and cable, etc.).

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