The new One Pound Coin is being lauded as the most secure, most difficult to forge, coin ever produced. One of the many features is the ‘hologram’ on the obverse, just below the Queen’s head. This is a small feature that shows a £ sign when viewed from one direction and a figure 1 when viewed from another.
Picture from the Royal Mint
However this isn’t a true hologram, rather it is a physical picture cut onto tiny ridges, one image is on one side of the ridge and one on the other. You can feel the ridges if you run a fingernail over the feature.
This type of picture is called an anamorphic picture, a picture that can only be viewed from a particular direction. The most famous example of this is the skull in Holbein’s picture ‘The Ambassadors’. However this type of anamorphic picture was developed much later and by the Regency was a children’s toy, and is described in The Boy’s Own Book published in 1834. The instructions are far from clear, if you would like to try and make one I give them here.
Naturally, as soon as I discovered these instructions I wanted to make one, so I began by working out the geometry.
Then I selected two suitable pictures (from the British Museum online catalogue) and printed them out.
These were then cut into correctly sized strips, that was what all the geometry was about, and pasted onto the base sheet.
When dry the strip was folded in a concertina fashion, the images are completely mixed up.
But viewed from the side one picture becomes clear.
And the other can be seen from the other side.
So to protect the most advanced coin of the 21st century, you need a child’s toy from the 18th!.