sparkles

Busy busy day, lots on at work. However +1/2 and I managed to sneak off for a birthday lunch here (it's +1/2's birthday tomorrow) which was delicious; cassoulet for +1/2 and Toulouse sausage and salad for me.

The picture is of the card that +1/3 and +2/3 made for us.

Look away now if you don't want to read random physics thoughts.

I love the sparkly/diffractive nature of whatever it is that covers the card. I think it's usually listed as 'holographic film' or similar and I suppose it could be: real holographic film has a spatial resolution of up to 4000 lines/mm so if you exposed it such that you ended up with a set of parallel lines spaced by about 1 micron you would get a transmission grating that would show the above. CDs are the same; they have a spiral track of pits and the pitch of the spiral is about 1.6 microns, the surface of the disk is then coated in a thin layer of metal.

That sounds a bit hard to make in volume and so cheaply, so I suspect the film is made by stretching metalized plastic film of some type very slightly to give lots of little parallel tears.