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Thread: identifying screw alloys?

  1. #1
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    Default identifying screw alloys?

    I have about 190# of assorted brass & bronze screws and bolts in various loosely labeled coffee-cans from my late father. The question is: which ones go to scrap and which ones are trustworthy? And how can I efficiently sort such a valuable hoard?

    I know from word-of-mouth that some of these came from the ashes of boats that burned, and some look unused. Most have various kinds of patina / corrosion / etc due to their provenance of being picked up off the ground in boatyards and salvage from rebuilds. (My dad was a depression kid, he picked up everything, I also have coffee cans full of steel bolts, hose clamps, compression fittings, etc, etc) I can buff these and generally identify the ones that are obviously brass, but the colors of the rest run the gamut and are often subtle. What to do?

  2. #2
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    Default Re: identifying screw alloys?

    Hmmmm. . . .I can almost always tell brass from bronze by nicking it with a file if it's not obvious immediately from the appearance. Silicon bronze is much harder and "stickier" whereas brass is more smooth and buttery.
    Maybe you can start with some known quantities and practice on them. I'll bet you see what I'm talking about pretty quick.

    Bronze is always better in salt water, but it may not matter quite as much there in the lake.

  3. #3
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    Default Re: identifying screw alloys?

    Brass or Bronze? Ok, I am shamelessly trying to move this old thread up in the newsgroup stack to see if I can get some more suggestions: Some newer screws have that reddish copper look that seems to say "Bronze," some weathered ones also have a reddish patina that also seems to imply more copper content. But when I scratch a bright facet on many of these salvaged mixed screws the color is incredibly similar. Is there any acid or other chemical that would detect the zinc in brass screws vs bronze? I want to dump all the brass ones in a heap to be used for trim or screen door hinges and leave the bronze ones for real work. Please advise.

    Ken

  4. #4
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    Default Re: identifying screw alloys?

    My dad never threw anything away either! I usually can pick brass out by its bright straw color. Bronze is more pink or red in color. Brass is also more brittle in feel when touched by a file. When corroded it has a distinct habit of becoming more eaten up than does bronze.
    All my scrap goes to the foundry.
    Jay

  5. #5
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    Default Re: identifying screw alloys?

    Would it be at all useful to throw the screws (in batches) into a tumbler such as what reloaders use for cleaning their used casings? Get them all to a uniform "polish", then see how they oxidize (or don't) from there. I'd be hard pressed to tell brass from silicon bronze from gunmetal from...

    Only thing I can tell you with any confidence is that manganese bronze (at least some alloys) and aluminum bronze will stick to a rare-earth magnet. Very lightly, but if the magnet is good, they'll stick. Aluminum bronze much more than manganese bronze --enough that I won't use aluminum bronze fittings near my compasses.

    Alex

  6. #6
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    Default Re: identifying screw alloys?

    This is another shameless attempt to move this thread up in the stack. Does anybody know of a good chemical zinc detector? Is there a chemical swab that would identify the brass? I spent some more time today with a power wire brush, and screws that definitely had that reddish bronze look when old and oxidized might look yellow brass after being buffed.

    Ideas?

    ken

  7. #7
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    Default Re: identifying screw alloys?

    http://www.bigdaddyscrap.com/prices.html

    190 lbs. X $1.35/lb. = $256.50.

    That will buy you some peace of mind.

  8. #8
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    Default Re: identifying screw alloys?

    Just grasping at straws: you might give Pete Langley a call, at Port Townsend Foundry. He might have some good way of telling one alloy from another. Throw them in a microwave and see if they glow purple (that was a joke! don't do it!), or some other hedge-wizard cantrip that'll let you sort them.

    Alex

  9. #9
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    Default Re: identifying screw alloys?

    Quote Originally Posted by Gib Etheridge View Post
    http://www.bigdaddyscrap.com/prices.html

    190 lbs. X $1.35/lb. = $256.50.

    That will buy you some peace of mind.
    +1
    Ah, a practical approach. Boring, but practical. I can't think of anything more exciting than testing 190 lbs of screws one at a time.

    http://forum.woodenboat.com/showthre...nze-from-brass
    In place of the back AR stone, you can get a nice 12" black granite tile for $6 at a home center.

    Chemical tests: I think that Si bronze would test same as pure copper, but the odds of pure copper screws are slim to none.
    https://www.koslow.com/manuals/1899-InstructionsV11.pdf

    For maybe $20k, you can buy an XRF gun and learn about X-ray fluorescence testing.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  10. #10
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    Default Re: identifying screw alloys?

    I'll refer again to that guy who makes boat building and repair videos for Jamestown distributors. He pointed out that when you drop brass and bronze screws on a concrete floor the bronze ones make a cleaner sharper ringing sound and the brass ones make a bit more of a dull ringing sound. (Makes sense, copper & tin vs copper & zinc.)
    I've tried it and it does seem to work. (I suppose I wouldn't bet my life on it 100% of the time though.)

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