Loyalty card code

Dave Ansell shows us a data demo...
14 April 2020

Interview with 

Dave Ansell, Sciansell; Adam Murphy


A store card being used in an experiment


For our first kitchen science demo of the show, Dave Ansell and Adam Murphy get to work with a rusty object, a loyalty card, and some sandpaper...

Dave Ansell - What you want to do first is get your rusty object and your sand paper and have something to catch the dust which comes off it cause that's what we're interested in and sand some of your rusty object onto your cup or your piece of paper to catch it with. So I've got an old barbecue, a very small round barbecue thing, which is very, very rusty cause it's been sitting in my garden for yonks, and just a piece of sand paper, which I picked out of the shed and I'm just sanding to produce a nice fine dust basically.

Adam - Well I've got an iron pot lid. It's got a bit of rust on the rim. I've got an old Emery board nail file because I couldn't find any sandpaper and a little plastic cup to catch it in. So now I have my plastic cup in front of me and it is full of a reddy-orange powder, which is the powdered rust. What do I do with it now Dave?

Dave Ansell - Put it onto the magnetic strip of your card very liberally and just kind of cover the basic strip with the rust powder. Ideally you want the finer rather than the really coarse powder and just spread it on so the whole of that strip is covered.

Adam - Okay, so I've got the card and I've got the cup full of the rust powder and I'm just going to start tapping it out gently. So I don't cover the entire house in rust.

Dave Ansell - And then once you've got it covered, just sort of gently tap the card. So the rust falls off.

Adam - Okay, so I've got something on this.

Dave Ansell - What can you see?

Adam - And what I've got is that the rust particles have formed kind of in stripes like you get on the back of a barcode packaging, like just loads of little stripes where there's rust and stripes where there's not.

Dave Ansell - That's brilliant. It turns out, it doesn't work in with every card. So you may have to try two or three until you get one which works.

Adam - Yeah, this is the newest one I have.

Dave Ansell - Yeah, they do tend to die after a while. Adam's one is working better than mine. I can see some stripes but it's uh, only in one corner of my card. But there are definitely some stripes on there. So what you're seeing is the magnetic strip is, as the name would imply, is magnetic and it stores information by having strips which are magnetic one way and magnetic the other way, and other bits, which aren't magnetic at all. What you're seeing is that the magnetic rust particles are only sticking to the parts which are magnetic. So you can visualize that magnetic barcode with your eyes

Adam - And then how would a card reader read any information off of that barcode type thing then?

Dave Ansell - If you move a magnet near a coil of wire, you basically create a little tiny generator and you generate a voltage in that coil of wire. So there's a coil of wire in the magnetic barcode reader and as you pull the strip past it it induces little tiny voltages in that coil of wire, which are electronics the computer can read as I think what's normally stored on there is a number on the front of the card.

Adam - And then is this the best way to store information or is it just a good way to store information? What is the best way?

Dave Ansell - It depends what you mean by best. It's quite a retro way of storing information. It's the same technology as cassette tapes to the older members of the audience or VHS video tapes all use the same kind of magnetic storage of data which are now having issues because after 30 40 years, the tape starts to degrade and the rust falls off the tape. And so it stops being able to store information and suddenly all those radio shows which everyone loved in the 70s becoming very hard to recover because even though the tape exists, the information has fallen off it, it's just a pile of rust at the bottom of the cap.


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