Why is printer ink more expensive than gold?

Kit Chapman from Chemistry World took on this chemical query from listener David. He explained to Izzie Clarke why this is indeed true...

Kit - Well, it is true, but bare in mind that gold is a really dense and heavy thing. So if you think about a pound of lead and a pound of feathers, a pound of feathers is going to take up far more space. But gold is not the most dense element, that's actually osmium, but it is dense so it takes up very, very, little space and that's why printer ink seems to be more because you get far more bang for your buck.

But printer ink is not the most expensive substance on Earth, that's a common misconception. The most expensive is californium, and this goes back to what we were talking about earlier with nuclear reactors and making things. What we actually do is we stick rods into our nuclear reactors; there are two of them that can make californium on earth - ones in Russia, ones in Oak Ridge in Tennessee in America, and it undergoes a series of what we call neutron capture reactions. A neutron gets turned into a proton and that moves it one place up the periodic table. Eventually we get to californium and that's really useful for things like space probes and exploring Mars.