Cleaning heavily tarnished copper

[Rrmuf]

Gotta try this. Is backset more effective hot than at ambient temp?

.... I have only tried it hot, but my sense is that the effectiveness does drop once it has cooled down.

[Twisted Brick]

Thank you, gentlemen.

[Demy]

If you want to experiment ok, I'll do it too but on a practical level no .... any acid solution will do the job (of course there is different power based on the type of acid) even lemon (read natural citric acid). After the acid passage I recommend a passage with a basic substance (for example bicarbonate) for the neutralization of residues that would produce a lot of oxide.

[contrahead]

I admit those copper tri-clamps looked sexy. I just assumed they were done by an electro-plating outfit and pretty pricy.

Sure, companies will preform copper electroplating for a price. But both crystal and liquid sources of cupric sulfate can be easily found and purchased. For better quality copper electroplating of smaller items at home though, one would want to acquire some cyanide based copper plating solution. “John Q. Public” could still purchase small quantifies of cyanide solution for hobbyist, jewelry and craft applications a few years ago; probably still can – I don't know.

Although some (but not all) forms of cyanide are poisonous, organizations like the EPA are much more focused and restrictive of electrolytes that use chromium trioxide; which is far more environmental persistent.

Cyanide-based solution would mainly be used for the underlying base coat, allowing the following copper acid or copper alkali layers to adhere better. Those trays and bins of new copper plumbing fittings you see in lumber or hardware stores are still relatively cheap, because they are fake copper. Just like our pennies now, those plumbing fittings are zinc alloy pieces that have been electroplated in copper-cyanide solution.

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This little .pdf is very informative -----> https://www.nmfrc.org/pdf/p1199l.pdf
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[Twisted Brick]

Thanks Contrahead. Very informative.