[zimmychild]

Scenario:

A bundle of money is rubber banded together in an aluminum cash box. This cash box is being stored in the basement of a home. This basement gets flooded. The money gets wet from said flood. The money is now brown and illegible.

Can someone explain this to me?

Is there a way to reverse this?

[Arkcon]

There are many possible reactions based on the circumstances.  Reversing them may be difficult, but the government should help, no nation wants its money to be useless so easily.  See what you can work with.

[Intanjir]

Is the money illegible simply because things are too brown or is the ink itself thoroughly blurred? Assuming that it is blurred then something had to compromise the ink.

I don't know of any compounds where aluminium contributes a hue.
However for Iron, the Fe³⁺ ion can contribute yellow or brown.
A solution of Fe(III) Chloride is clear yellow, and we are all familiar with brown iron rust.
Iron is a common pigment for inks so I dripped some 30% HCl acid on a $1 note.
The liquid turned yellow where it contacted the grey ink on the front of the bill.
When neutralized it became brown. The grey ink became green as a result of all of this and remained legible. The green ink in general was unaffected.

So US Currency probably uses iron in its ink, and it is plausibly the mobilization/reaction of this which accounts for some of the faded legibility and much of the brown.

However unlike in strong acid, iron isn't particularly soluble in even strong base.
So lime water directly dissolving the iron seems unlikely.
I also tried droppering on NaOH solution and nothing visible happened.

If it is illegible then the green ink must also have been mobilized, so a natural hypothesis is that the binder in the inks was compromised and not the pigment.
The jobs of the binder are to hold the ink to the paper as well as allow the ink to be suspended in solution.

Naturally the binder used in our currency is not water soluble, and given that neither strong acid nor strong base compromised the green ink, I am at a loss.

[Borek]

At least here damaged bills - as long as there is no doubt about their legality - will be replaced by the national bank.

[zimmychild]

The bills are just stark brown. They look like brown paper and are completely illegible. The bank can do nothing because of this. It's not my money, and I'm not particularly concerned with "fixing" it, I was simply curious as I thought the reaction was odd. Thanks for the responses!

[Intanjir]

Ahh, perhaps they simply absorbed enough sufficiently small bits o dirt. I'm surprised that it didn't simply wash out enough with soap.

Anyways, the term for scenarios like this is apparently mutilated currency.
https://en.wikipedia.org/wiki/Mutilated_currency

If the bank wasn't able to process it then they should have advised the owner that they can simply send it to the Bureau of Engraving and Printing.