Plastic money: how Australia made polymer banknotes

The full story

This is the episode's narration, word for word. Headings jump to that point in the video.

The question 0:00

Scrunch an Australian banknote into a ball, and it springs back. Try to tear it, and it's hard even to start. That's because it isn't paper; it's plastic. So why would a country print its money on plastic, and how could a clear little window stop a forger? The answer starts with a bakery.

The bakery 0:22

In 1966, Australia switched to decimal currency, with new notes that were meant to be very hard to copy. Within a year, forged ten-dollar notes began turning up in large numbers. They had a tell. On the back of the note was a building, the Times Bakery, and on the fakes, its horizontal lines didn't line up with the edge of the wall. Police feared a million dollars' worth were circulating.

If you can photograph it 0:51

How do you forge a paper note? You photograph it, make printing plates from the photo, and print. Almost everything you see on a paper note, the colours, the fine lines, the portrait, is a pattern of ink, and a camera records patterns of ink. Raised printing and a metal thread made forging harder, but not impossible. And by the late 1960s, the Bank was worried about something worse on the way: the colour photocopier.

Turning to science 1:20

In 1967, ten people were charged, and seven were eventually jailed. In the end, far fewer turned up than feared: about a hundred and twenty thousand dollars' worth had been detected by 1974. But the Reserve Bank's Governor, Nugget Coombs, drew a bigger lesson. Forgers had caught up with the best printing money could buy. So he turned to science.

Thredbo, 1968 1:48

In 1968, the Bank and the CSIRO brought scientists together at Thredbo, in the Snowy Mountains. The invitations were dated the first of April. Most were physicists, plus two chemists: Sefton Hamann and David Solomon. David Solomon later recalled a point made by someone from Kodak, which framed everything after: if a note can be photographed, it can be printed, and forged.

Beat the camera 2:17

So the challenge was to put something on a note that a camera can't capture. A camera records one view, from one direction. So use a feature that looks different when you change how you look at it. The team called these optically variable devices: anything that changes its appearance when something outside the note changes, like the angle you view it from. In 1972, Hamann and Solomon proposed putting them on a plastic note; the idea of using diffraction gratings came from a former Chief of CSIRO Radiophysics, Dr Bowen, and Hamann took it up.

A rainbow on purpose 2:57

The device that won works like the rainbow on the back of a CD. A CD's tracks are evenly spaced rows, and light bouncing off them adds up only in certain directions. In those directions, the waves from neighbouring grooves are a whole number of wavelengths out of step, so they reinforce: in the first, exactly one. Each colour has a different wavelength, so each colour leaves at its own angle. With grooves a thousandth of a millimetre apart, and light shining straight on, the deepest violet leaves at about twenty-two degrees, and the deepest red at about forty-nine. It's called a diffraction grating, and tilting it changes which colour reaches your eye.

Why a copier fails 3:42

Now put that under a photocopier. The copier sees whatever colour comes back at its one angle, and prints that colour in flat ink. Flat ink looks the same from every angle, so the copy doesn't change when you tilt it. To fake the real thing, you'd need grooves about as fine as the wavelength of light. Ink can't do that, which is why the project's records say gratings resisted copying by photography and by printing.

Why plastic 4:12

But a grating works far better on a smooth surface, and paper is a mat of fibres. The Reserve Bank's own history counts that as one more reason to build the whole note on plastic film. That brought a second weapon: a clear window. A window means a forger must also print on clear plastic, and in the 1970s nobody sold a laminate like the one CSIRO made.

Stretched both ways 4:38

The film they settled on is polypropylene, the same plastic as many bottle tops and storage boxes. Freshly made, its long molecules are a tangle, like a bowl of spaghetti. Stretch it, and the molecules untangle and line up along the pull. So the film is stretched in two directions, along and across, and the result is clear, and tough in every direction. That's biaxially oriented polypropylene, chosen for its resistance to folding and tearing. Today, it starts as pellets, melted and blown into a bubble three storeys high.

The team 5:17

From 1974, David Solomon led the CSIRO side, with a pilot plant at Fishermans Bend in Melbourne. Sefton Hamann worked on the optics, and Robert Lee developed the theory for designing the gratings. Mario Girolamo worked on the plastic. Graham Quint and Alan Wilson developed an electron-beam system to write the fine grating patterns. At its peak, seventeen CSIRO staff worked on it, alongside the Reserve Bank's own engineers and printers.

Building a note 5:51

So how does clear plastic become a note? First, white ink goes on both sides, except where the windows will be. Then the colours are printed on both sides at once, so the two sides line up exactly. That allows a trick: half a pattern on the front, half on the back, which only completes when you hold the note up to the light. Then comes raised ink, pressed on from engraved plates so you can feel it, and a protective overcoat.

Testing money you can't spend 6:22

You can't field-trial a banknote, so the team devised a tumble test. They weighted test notes, then tumbled them in a drum with fake dirt, plastic beads and artificial sweat. It turned out to predict real wear remarkably well. And so a lost test note couldn't be spent, they printed them as three-dollar and seven-dollar notes, which don't exist.

Twenty years to January 1988 6:46

It took twenty years. Early test notes didn't recover from folding as well as paper, and the gratings were hard to make stick. Solomon also blamed a cautious banking culture. In 1985 the Bank chose a trial: a commemorative ten-dollar note for the 1988 Bicentenary. It was issued in January 1988, with a clear window and a grating image of Captain Cook. Others had tried plastic-like notes made of fibres, in Haiti and the Isle of Man, and they smudged and failed. This was the world's first note printed on a non-fibrous plastic film.

Built to last 7:27

Between 1992 and 1996, every Australian note switched to polymer, the first full series in the world. Paper notes had worn out in six months to a year. Plastic doesn't soak up moisture or dirt the way paper fibres do. Polymer fives and tens last a little over five years, twenties about ten, fifties about fifteen. Each plastic note costs more to make, but the Reserve Bank estimates the switch saved close to a billion dollars over twenty-five years. Worn-out notes are shredded and melted into pellets for other plastic products.

Did it stop the forgers? 8:08

The Reserve Bank counts forgeries per million notes in circulation. The 1966 bakery fakes were feared to run to several thousand per million. In the early 2000s, Australia's rate was about five to ten. It peaked at under thirty in 2015; in the years since, the euro area has reached about fifty, and Britain about a hundred and forty. Polymer isn't unbeatable: plastic fakes rose from 2010, which helped drive a new series with a window from top to bottom. By 2021, the rate was down to nine per million.

Plastic goes global 8:48

In 1996, the Reserve Bank and a UK film maker set up a joint company, Securency, to sell the plastic film to the world. New Zealand switched entirely to polymer in 1999. By 2009, Securency's film was used for banknotes in twenty-seven other countries. Canada began issuing polymer notes in 2011, and the Bank of England in 2016.

The dark chapter 9:21

Some of that overseas business broke the law. In 2009, The Age newspaper reported that agents' payments may have funded kickbacks to foreign officials. In 2011, Securency and the Reserve Bank's own printer, Note Printing Australia, each pleaded guilty to conspiring to bribe foreign officials: between them, in Indonesia, Malaysia, Vietnam and Nepal, between 1999 and 2004. They were the first prosecutions under Australia's foreign bribery offence. Together, the companies paid more than twenty-two and a half million dollars in fines and penalties, and court orders, which the Bank hadn't sought, kept the pleas secret until 2018. The Reserve Bank sold its share of Securency in 2013.

Who invented it? 10:17

So who invented plastic money? Not one person. The Reserve Bank asked the question and funded much of the work, CSIRO put in its own resources too, and the Bank's engineers and printers turned it into a product. CSIRO's chemists and physicists, led by David Solomon, with Sefton Hamann, Robert Lee and many others, did most of the inventing, working with the Bank's own team; the patent was joint. Others had tried plastic money first, but this was the version that worked, and it came out of Melbourne.

The next question 10:53

Next time, a giant dish in a sheep paddock near Parkes, and the day the world watched a man walk on the Moon. How does a dish hear a TV camera on the Moon, and who really carried which minutes?

Sources

Every factual claim in the episode is tied to one of these. Spotted an error? Tell us.

1. RBA Banknotes: "List of Security Features" — banknotes.rba.gov.au
2. RBA Banknotes: "Production" (incl. production video transcripts) — banknotes.rba.gov.au
3. RBA Bulletin, September 2019: "A Brief History of Currency Counterfeiting" — rba.gov.au
4. RBA Museum: "Introducing Polymer Banknotes: 1988" (display page, archived 2019) — web.archive.org
5. CSIROpedia, Colin Ward: "Polymer banknotes" (2011; Wayback copy) — web.archive.org
6. Australian Science and Technology Heritage Centre, University of Melbourne: CSIRO… — austehc.unimelb.edu.au
7. HyperPhysics (R. Nave): "Diffraction Grating" — hyperphysics.phy-astr.gsu.edu
8. OpenStax, University Physics Volume 3: "4.4 Diffraction Gratings" — openstax.org
9. Wikipedia: "Polypropylene" (section: Biaxially oriented polypropylene) — en.wikipedia.org
10. DoITPoMS, University of Cambridge: "Crystallinity in Polymers" — doitpoms.ac.uk
11. RBA Banknotes: "Top-to-bottom window" — banknotes.rba.gov.au
12. RBA Banknotes: "History of Banknotes" — banknotes.rba.gov.au
13. Wikipedia: "Polymer banknote" (history; timeline of adoptions) — en.wikipedia.org
14. RBA Bulletin, December 2019: "A Cost-benefit Analysis of Polymer Banknotes" — rba.gov.au
15. RBA Banknotes: "Questions and Answers: Production" — banknotes.rba.gov.au
16. RBA Bulletin, September 2019: "Survival Analysis and the Life of Australian Banknotes" — rba.gov.au
17. RBA Banknotes: "Counterfeit Statistics" — banknotes.rba.gov.au
18. RBA Bulletin, March 2019: "Recent Trends in Banknote Counterfeiting" — rba.gov.au
19. RBA Bulletin, June 2022: "Recent Trends in Banknote Counterfeiting" — rba.gov.au
20. RBA Media Release 2009-11: "Statement Concerning Securency International Pty Ltd" (23… — rba.gov.au
21. RBA: "Chronology: Events related to charges against Note Printing Australia and… — rba.gov.au
22. Bank of Canada: "Backgrounder on Canada's new polymer bank note series" (June 2011) — bankofcanada.ca
23. RBA Media Release 2018-29: "Guilty Pleas made by Note Printing Australia and Securency… — rba.gov.au
24. Supreme Court of Victoria: R v Note Printing Australia Limited and Securency… — web.archive.org
25. RBA Media Release 2013-02: "Sale of Securency" (12 February 2013) — rba.gov.au

Researched and scripted with AI assistance, fact-checked claim by claim, with synthetic narration and diagrams drawn in code. How we make episodes.