Platinum or white gold ?
White gold is an alloy of three different metals including Palladium and an alloy to harden the final result. It is more resistant and less pliable than Platinum.
Platinum has a higher degree of purity and a much higher melting point than gold. It is best suited for intricate work with lots of soldering such as large classical pieces constructed out of fine wires that will not be submitted to much wear and tear. Solitaires and eternity rings are more resistant in white gold than platinum! Both metals are finished with a coating of Rhodium, so both look absolutely the same!

White or Yellow gold ?
Cool or warm, matching the other jewellery you already have.
Diamonds set in white gold will look bigger and brighter. Yellow gold will place more emphasis on the design, downplaying the diamonds a little and each individual small diamond will be more apparent to the naked eye.
Yellow gold is advised for fragile coloured stones such as emeralds.
Blue sapphires look nicer in white gold. Rubies are more suited to yellow gold.

Hand made or a casting ?
Castings are cheap, more breakable, less easy to polish to a high gloss, prone to pinpoint blemish they also tarnish easier. Hand made jewellery means the alloy has been forged, forcing the air molecules out of the metal. It is less prone to metal fatigue, easier to resize, has more gloss when polished. It is therefore best suited for quality work intended for high quality precious stones.
Castings are not applicable for exclusive, unique jewellery; it is used for large quantity productions. Branded jewellery is nearly always produced by casting.

Why not copper or plastic ?
Copper is very, very hard! It is used in alloys to harden other metals. It tarnishes easily and is not suited for quality jewellery. Coated with a gold plating it is sold as "18kt gold" to tourists on Mt Vesuvius!
Plastic or acryl, wood, ivory, mother of pearl, onyx or hematite; we can use all sorts of "exotic" materials to create more daring designs!

Insurance or locked in the safe ?
I don't understand the question or should I rephrase it: wear it or hide it?
Never insure you jewellery together with oriental rugs, paintings and furniture.
Make sure you have an "All Risk" jewellery only contract with no "mysterious loss" clause. Refuse contracts that let the insurance company supply a replacement for your stolen jewellery! Insure for the replacement value, not for appraised value in auction or by the company's expert.

Should I trust a local jeweller to resize my diamond ring ?
99.9% YES!
This is the biggest myth of all in the jewellery trade: this guy changed my diamond!
Most jewellers are honest hard working people, their suppliers entrust them with over a hundredfold the value of your single diamond!
Obviously there are some crooks out there who will swap your diamond for a less valuable stone. Luckily for all of us they are known to the insiders so be candid and ask around, honest people will steer you clear of the rogues.
So why the myth? Mostly because of ignorance and fear, like fundamentalism and racism. How well do you know your diamond? We never let a customer leave the store without a complete knowledge of his purchase.
A string of pearls is indeed shorter after restringing, there are no pearls missing but the string was stretched out by wearing!

How often do I need to clean and check my jewellery ?
I recommend once a year for eternity rings that have diamonds all around and are worn every day. Jewellery that is not worn daily should be checked every two years and whenever you feel a stone is loose or you notice deep scratches on the underside of the ring. The post of your earrings should be cleaned very often with some disinfectant. Your watches' leather straps may be soaked with perspiration which will harden it and cause it to crack; replace it once a year to avoid the risk of loosing the watch unexpectedly.
Do not boil your valuable jewellery in a pan with some household detergent!