How can I easily remove black from cupronickel after heating it?

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Discussion Overview

The discussion revolves around methods for removing black oxidation from cupronickel quarters after heating, particularly in the context of numismatic restoration and metalworking techniques. Participants explore various chemical solutions and their effectiveness in cleaning the metal without extensive manual polishing.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant mentions using Sparex no.2 for silver but finds it ineffective on cupronickel quarters, seeking alternative solutions.
  • Another participant points out that the cupronickel alloy composition may complicate the electrochemical reactions during cleaning.
  • Several solutions are proposed, including citric acid for mild action and phosphoric acid-based soldering flux for medium action, with recommendations for cold baths and agitation rather than quenching.
  • A participant expresses a need for a solution that minimizes hand polishing after shaping the quarter, indicating that the current process is labor-intensive.

Areas of Agreement / Disagreement

Participants present multiple approaches and solutions, but there is no consensus on a single effective method for cleaning cupronickel quarters after heating. The discussion remains unresolved regarding the best cleaning technique.

Contextual Notes

Participants express uncertainty about the appropriateness of various cleaning methods for numismatic restoration and the specific effects of different chemical solutions on cupronickel.

Letsurf
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So I'm using sparex no.2 to remove the black from silver after I heat it. I just quench in the sparex solution and it removes the black instantly. I'm trying to heat a quarter and use sparex to remove the black but it's not working. The quarter is cupronickel which is a mix of 75% copper, 25% nickel. Any idea what solution I could use to remove the black from the cupronickel after heating it?
 
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Letsurf said:
75% copper, 25% nickel
Not in Wiki's description of U. S. "sandwich" quarters. You've got two different alloys in a bath committing electrochemistry on each other.
 
So what is the solution?
 
Depends on what you're trying to accomplish. If it's some sort of numismatic restoration, what is and is not acceptable is not something I know anything about.
 
Citric acid - mild action .

Phosphoric acid based liquid soldering flux - medium action

Cold bath and soak in each case with agitation . Do not quench .

Several stronger solutions are available but probably not nescessary .

Citric acid is usually quite adequate for removing oxides from a one time heat of clean metal .
 
Nidum said:
Citric acid - mild action .

Phosphoric acid based liquid soldering flux - medium action

Cold bath and soak in each case with agitation . Do not quench .

Several stronger solutions are available but probably not necessary .

Citric acid is usually quite adequate for removing oxides from a one time heat of clean metal .

Thanks for the tips. I heat, bend, reheat, bend the quarter to make rings. Is there something I can quench it in during this process so when I'm finished it will require minimum hand labor to polish? By the time I'm done shaping it now it is black from the heat and takes several minutes of intense hand polishing with steel wool to get the black off. With silver the sparex makes it a very simple process so I'm just looking for something I can use with the modern quarters that will make it easy.
 

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