A few button related gleanings from t'internet.
Button is derived from the French "bouton" meaning bud or knob. They've been with us a long time with shell examples found 5000 years ago from the Indus Valley Civilisation. It's thought that they were used for ornamentation rather than for fixing garments in position. The theory goes that the buttonhole is down to the Crusaders bringing the idea back to Europe from the Middle East in the 13th century.
Buttons are measured in lignes which is abbreviated to L. 40 lignes is equivalent to 1 inch.
Not everyone is keen on the humble old button. It will come as no great surprise to learn that the Puritans condemned them as sinful. They are regarded as an outward sign of pride by the Amish so their use of them is sparing and they tend to favour pins over them. Those who are phobic about them are suffers of koumpounophobia.
Men's clothes traditionally button down the left side as men were expected to dress themselves whereas women of means were dressed by servants facing them which is why they are on the right side. Button down collars were worn to stop them flapping up in the face when horse riding.
As for the button necklace...well that might just have come home with me after my weekend charity shop trawl. A little lovely for £2.