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topic 61111

C377 Brass Forging turned silver from Scotch-Brite Polishing


May 20, 2020

Q. I have a forged brass (C377 - confirmed with a Niton Gun) door threshold that arrived in my shop with some surface marring. I polished the surface, by hand, with a red scotch-brite pad and the surface is now a bright silver color.

61111-1

Is there a solution or polish I can purchase or make in order to restore the original, uniform yellow color?

Brian Mathey
- Pleasant Prairie, Wisconsin USA


May 2020

A. Hi Brian. As someone who has long argued against trying to judge what metal something is made of from its appearance, I'm certainly not about to look at a picture and then argue with a Niton Analyzer ... but have you analyzed against the possibility that while this threshold is made of C377, it might have a finish of bright nickel plating followed by brass plating, a PVD finish, or electrophoretic lacquer?

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading


May 21, 2020

Q. Hi Ted - thanks for the response!

It does look like this material has been plated or lacquered. It's very easy to remove the top layer, by hand, with scotch brite pad.

It looks as though I'll have to finish polishing this part to remove the marring and light scratches and then have it replated.

Any thoughts or recommendations on the above plan?

One other question. Why would a manufacturer make this threshold from C377 and then plate it with nickel and plate it again with brass? For increased toughness on the finished material? Door thresholds take quite a beating and I wonder if this type of fabrication is standard practice?

Thanks again!
Brian

Brian Mathey [returning]
- Pleasant Prairie, Wisconsin USA


May 2020

A. Again, Brian, I'm not claiming that it IS nickel plated, only that it looks like it might be. I would think there should be a way of figuring it out, maybe with your Niton Analyzer. Until you know what it actually is, it's hard to figure out how to restore it to what it was.

I'd guess that most door thresholds are relatively cheap anodized extruded aluminum rather than forged brass, but I'm not privy to any experience in that industry, and things may be very different for high traffic commercial thresholds than what I'd surmise from the stock at Loews and Home Depot :-)

My guess would be that it's difficult to get what the seller feels is a bright attractive finish from polishing the brass forging, so they nickel plate it and add a color layer through some technology. I do know that this approach is widely taken with decorative plumbing fixtures (brass plating or brass colored finishes on solid brass faucet sets), so I suppose it could be done on thresholds.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading


May 23, 2020

A. Brian

The countersunk hole appears to show a silver metal as opposed to brass. If you did not polish it, I would suspect Ted is on the right track that it is anodized aluminum.

Are the ends of the threshold silver colored? It is easy for manufacturers to anodize long extrusions, then cut to length knowing the ends and holes will not show once in place.

Willie Alexander
- Green Mountain Falls, Colorado

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