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Comment by cperciva | Hacker News Reader

Paper doesn't last very long. Five year from now, the old bills will still be in circulation, but they'll be uncommon. Ten years from now, any time you try to use one of the old bills, the merchant will look at it very carefully before accepting it.

The trick is to keep security measures a decade ahead of counterfitters, so that the only counterfit bills are the ones which are antique enough to attract extra attention.

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I had the cashier in a toll booth refuse to accept a perfectly valid old-style $20 bill last week. I asked him what was wrong with it and he whipped out a new-style one and said "they're not the same, it's fake."

He even halfheartedly threatened to call the police.

Dollar bills are actually made from more than just wood pulp, they also include cotton, silk and linen -- along with red/blue fibers inserted to create texture.

According to the federal reserve, bills have the following lifespan before they wear out:

$ 1.....22 months

$ 5.....16 months

$ 10.....18 months

$ 20.....24 months

$ 50.....55 months

$ 100.....89 months

http://www.federalreserve.gov/generalinfo/faq/faqcur.htm#13

89 months is over 7 years.

And those numbers assume they are in circulation.

So it's perfectly plausible to have the old $100s in circulation for the next decade, assuming some are kept in security boxes, etc.

But I guess they are planning for after 2025 to have some kind of lock against fakes finally.

> Paper doesn't last very long.

This is an argument for polymer bank notes. Australia has these and they're very durable.

Or an argument against them; if they stay in circulation forever it gives counterfeiters longer to work on them.

They have transparent sections, holograms, angle variable colors - they are extremely difficult to counterfeit. US notes you can copy with half a carved potato

I'm going to call shenanigans. Do you have a source for that claim. I'm not disputing the quality of Australian currency, but I don't see how American currency is trivial to counterfeit.

I've heard of cashiers being fooled by colour photocopies of paper bills. I've never heard such a story about plastic currency.

> US notes you can copy with half a carved potato

kjhughjkjh, I have a call for you on line one. claims to be from the Secret Service? ;)

Does the DMCA ban potatoes now ?

Except that the polymer used is hard to obtain and the process to print on it is difficult to achieve without some serious equipment and know-how. Some of the notes have now been in circulation for more than a decade without realistic forgeries appearing.

So whereas a passable USD forgery can be made with a photocopier and some soft paper, the polymer notes are so expensive to reliably forge that it's not worth the effort. In practice Australia has very little in the way of forgery and it's usually detected by merchants almost immediately.

The main blight on polymer notes is that the company (Securency) which manufactures them has been accused of bribing officials in various countries to switch to polymer notes. Given that Securency is half-owned by the Reserve Bank of Australia, it is tremendously embarrassing.

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