David Williamson digs out some tips for those diamond geezers inspired by Lembit Opik's recent marriage proposal. It's only rock 'n roll but we girls like it...
THE next time you look at weather presenter Sian Lloyd you may be dazzled by a heart-shaped engagement ring presented to her by Montgomeryshire MP Lembit Opik.
They are a cracking couple, but the most famous Welsh-Estonian in the House of Commons may have just discovered why men and diamonds have long had an awkward relationship.
It can be irksome to discover that the gleaming stone on your beloved's finger is now her best friend, when you thought that was your title.
But the engagement ring - an invention introduced by Pope Innocent III at the Fourth Lateran Council in 1215 to extend the waiting period between betrothal and marriage - is something the woman you want to wed will have imagined glinting on her finger at least three times a day since the age of four.
If you do not buy her one now, it is unlikely that she will support your future suggestion that you celebrate your 50th birthday by buying a Harley Davidson.
Do not under any circumstances consider purchasing an isotropic crystal with a refractive index of any other than 2.417. Your fiancee will be quick to point out that the rock you have presented her with is not technically a diamond, and she may revoke permission for you to join your friends on that research trip to Las Vegas.
'What difference does it make?' you may cry, quite reasonably. But diamonds exert a logic-bending power, even on people who should know better than to get giddy about bling.
Don't look to the wisdom of Confucius for help. Some 2,500 years ago he said, "Better a diamond with a flaw than a pebble without."
Thankfully, discrete (small) diamonds are fashionable among women of style and taste. Generally, one carat represents a diamond with a diameter of 6.5mm; so if your fiancee asks for a million carat diamond, you can with all honesty say you doubt she would have the strength to lift a four-mile-wide rock.
Engagement rings can be bought on the internet for £149.99, but pink diamonds sell for $1m per carat.
The man to blame for this expensive custom way of pledging undying devotion is Archduke of Austria Maximilian I who solidified the Habsburg empire by giving one to Mary of Burgundy in 1477.
But modern engagement rings only became popular when the De Beers diamond cartel and the NW Ayer advertising agency transformed a moribund market in 1938 by presenting the precious rock as the ultimate gift of love. This was done by draping movie stars in diamonds and, later, selling the myth that "a diamond is forever".
This claim is a bit of an exaggeration because, according to the terrific Wikipedia encyclopaedia, 18th century scientists successfully set fire to diamonds, thus proving that these beautiful objects the Greeks believed were the tears of the gods were made of carbon.
But if the extreme pressures and sweltering environment of pre-married life are getting you down, look to the ring on your betrothed's finger for encouragement: It under exactly these same conditions of exceptional duress that something as mystifying, sought-after and brilliant as a diamond is born.