How long can a copper coin keep its red luster(RB)?

Some days ago, I saw an RB coin. RB is not important but the coin itself: it's 1824-R Brazil 40 reis which means the coin has kept 200-year red luster. It's amazing. I'll send it to N/P. Maybe you think it's fake, I have more examples like a Sweden 1/2 Skilling, 1801:

https://auctions.stacksbowers.com/lots/view/3-GO4CX/sweden-12-skilling-1801-pcgs-ms-64-rb-gold-shield

Like a Holland 1 duit, 1780:

https://www.numisbids.com/n.php?p=lot&sid=5058&lot=1082

As a result, I wonder the year of a coin's red luster. I see, maybe 250 years? But some 16-century coins seem to be RB coin too:

N#56935

More than 400 years…

So I want to know how long time the luster can be kept. To give the question in a proper and valid situation, I must say the question is about a coin's fate.

Technology to make a coin affect influence the coins' luster. The coin flan is first. In my country, coins called Szechuan 200 cash, 1926 is an example. Half of them are made of bad metals, mainly copper, which called ill copper. Although UNC ones are even BN (soil color or milk chocolate color in fact). They are BN forever. Half of their flans are made by cast, which are easier to oxygenate. And we can now, cast in wethot air, hammered in acid and milled by weak force can also make coins BN when they were made first time. Also about keeping situation about the coins, some coins are in good condition and some varieties are not. Coins in certain time or certain space even mostly have been rusted. And number of coins are also important, if the coins are little in scale, and not emergency coins or trail strike dies, also called pattern, they are always in good condition and sometimes RB. And the coins are in large scale, coins in mid of coin roll will keep color even RD.

So, the questions are:

1. Which's the oldest RB coin you've seen? (with pics)

2. Which's the oldest light yellow brass coin you've seen? (with pics)

3. Which's the oldest BN coin without environmental damage? (I see, maybe a classic coin.)

Hi Kivy.  Before going too deep down the rabbit hole, it may be helpful to understand that different TPG's (Third Party Grading) companies have very different thresholds for awarding the RD, RB, and BN designations.   So what you or I may call “BN” may not be what PCGS, NGC, CACG, ANACS, ICG, (or the large number of additional TPG's out there) would call it.  See the references below for what PCGS and NGC's thresholds are.

Since copper itself is such a reactive metal I don't think you're going to find a hard cut-off date.  Couple this with the fact that these designations are not standardized across TPG's and it makes the questions even harder to answer.

References:

PCGS:  “What Do RD, RB & BN Grading Designations Mean on Copper Coins?”

https://www.pcgs.com/news/rd-rb-bn-grading-designations-on-copper-coins

NGC:  “Learn Grading: What are BN, RB and RD?”

https://www.ngccoin.com/news/article/6605/learn-grading-red-brown-copper

These coins probably were “cleaned” at some point (like it was done in many coin cabinets over the centuries) resetting the surface oxidation a century or two.

But to your question, under the right circumstances it can stay red indefinitely (in outer space for example), or very long if it is stored in a place with low moisture, low oxygen, no sulphur, no handling, no sunlight, stable temperature etc. pp.

I'm skeptical of your claim of them being “cleaned”, even from cabinet friction. The coins shown have red only in the recessed areas, which is the opposite of what you'd expect from cabinet friction or a surface wipe, since that would mostly affect the high points. That would also likely leave hairline scratches whitch would typically get a copper coin to details grade. If the friction or cleaning did reach the low points of the coin I can't imagine that cleaning would not have serious negative effects on the surface quality of the coin. And if the coins were dipped (I know you're not proposing this idea but I'm just covering some bases) they'd likely have an off pink color. I think the last coin the OP showed was not an original red coin (the one from the 1500's), but the others seem original in the sense their surfaces had never been interrupted to create a new layer of red copper.

I would say at least 160 years as there are 1860 UK pennies and farthings that blaze lustre. For copper I am not sure, but oldest I have seen are blazing shiny US cents from about 1810.

My oldest that is red brown

Looks lighter in real life

For some lustre these 1860s farthings, but I have seen 1797 Cartwheel pennies and tuppences with blazing natural lustre.