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  1. #1
    Join Date
    Mar 2013
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    south coast Australia
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    Default Acid resistant brass screws

    I tried to turn some brass wood screws a copper colour by putting in a weak acid solution (to eat the zink away) in order to match a copper alloy casting. The weak acid made no progress at all so I upped the strength and left them in over night. Next morning still bright brass colour, so went over them with 000 steel wool in case they had some sort of protective coating and repeated the process --- still nothing. In desperation I took to them with Hcl acid and still nothing. The screw are very old perhaps 40 to 50 years, but I have never come across any brass before that is so acid resistant.

    Has anyone ever encounted this type of resistance? Normally you only have to show acid to brass and it turns red in fright.

    Bruce

  2. #2
    BobL is offline Member: Blue and white apron brigade
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    Feb 2006
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    Perth
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    Default

    Are you sure they are brass. If they are bronze, especially Al bronze that is resistant to HCl at room temp.
    The HCl should have an effect at higher temperature or try some Nitric or sulphuric acid.

    see The Hendrix Group > Resources > Material Property Data > Copper and Copper Alloys > Copper Corrosion Resistance Data

  3. #3
    Join Date
    Mar 2013
    Location
    south coast Australia
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    Default

    Thanks for the reply. I suspect you're on the right track, and I hadn't thought of that. The outer pack is missing so nothing to go by. Looking through the other packets of brass screws (all marked and of the same age) unsurprisingly they are all tarnished, but the screws in this pack are all shiny, and they wouldnt be the case if they were brass.
    Bruce

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