Being called ‘a diamond in the rough’ is actually quite a compliment because it infers that with a bit of work and a good polish, the end result will be a real gem. It’s also the truth about stones, of course. I’ve watched more than one documentary on mining for gems and I’m always impressed that the miners can pick up a chunk of dirt – literally – and go bananas about it because they can see exactly what it is – a diamond (or sapphire or…) in the rough. I always imagined that gems come out of the ground the colour they are when we buy them all cut and polished, and some do, but not all.

Aquamarine, for example, is quite a milky stone, but with heat treatment to get out the milkiness and the yellow tinge, we end up with the most wonderful clear stone that we all know and love. Tanzanite came as a huge surprise to me because when it comes out of the ground it’s an uninspiring brown (see? how did the guy who dug up the first Tanzanite know it would be something wonderful if he heated it??) and then with heat treatment we get those wonderful blue and mauve stones that we all want. Rubies and sapphires have been heat treated for centuries, maybe as far back as the Romans even, but really it became common practise at the beginning of the 20th Century. Apparently rubies have a blue core which disappears permanently when heated making the rich, gorgeous pigeon’s blood red gem.

Aquamarine; rough, heated, cut and polished.

I didn’t know that when amethyst is heat treated it goes paler rather than darker, and with even more heating it turns into citrine!

But as I said, not all stones are heat treated. Apparently emeralds are never subjected to heat treatment but very often they are soaked in cedarwood oil which, at a molecular level, fills any surface-reaching inclusions. The oil isn’t permanent and might need refreshing but only after many, many years. So here’s a stone that you would go bananas about when you dug it up, certainly. As an aside on the subject of emeralds, Polly was introduced, many years ago now, to an old gent in Rome who could ‘read’ emeralds. He could look at an emerald through his loup and tell you where it came from, right down to the mine, and how old it was. I expect this is something to do with knowing that the most precious and sought-after emeralds come from three countries; Brazil, Colombia and Zambia, and they’re all a slightly different colour because the trace elements responsible for the stone’s colour are different in each country, which would certainly help with pinpointing the mine, for instance… but what a great party trick that would be!

Along with emerald, garnet, peridot, chrome tourmaline and opals are some of the other stones not typically heat treated but of course they are cleaned and cut and polished to reveal their beauty which is, in its way, another form of treatment.

A Swiss couple really perfected the art of heat treating sapphires and rubies, particularly, and apparently at the end of her life, the wife of the couple felt a lot of guilt for making ‘counterfeit’ stones. But I think her guilt was misplaced; did the Japanese potter who discovered raku firing then sell counterfeit pottery because it was no longer just clay? No, of course not! I think the good lady and her husband are owed a huge debt of thanks for finding a way of producing stones of such astounding beauty out of a lump of rock.

And anyway, a magpie never asks ‘How came this beautiful bauble?’ It just scoops it up, chattering with glee, and flies it off home to add to its collection of other wondrous things. Sensible bird.

A diamond in the rough

As good as gold