Hardness and toughness
The Mohs scale is the most commonly used scale used to measure gem and mineral hardness. Corundum (ruby and sapphire) are relatively hard gemstones —9 on the Mohs scale. They have excellent toughness and no cleavage, which is a tendency to break when struck. This makes them a great choice for rings and other mountings subject to daily wear.

Stability
Yellow sapphires are stable under normal wearing conditions, which means that they’re resistant to the effects of heat, light, and common chemicals. Fracture-filled, cavity-filled, and dyed yellow sapphire stones can be damaged by even mild acids like lemon juice.

Cleaning
Yellow sapphires are extremely durable and hence they are able to withstand a large number of cleaning techniques.

Here, warm soapy water is the safest course of action. Ultrasonic cleaners or steam cleaners are ideally safe for untreated, or heat-treated gemstones. Fracture-filled, cavity-filled, or dyed yellow-sapphire stones should only be cleaned with a damp cloth.

Some people take their gemstones and jewellery to a professional to have it cleaned, but yellow sapphire or ‘pukhraj’ gemstones can just as easily be cleaned at home.

1.   In a bowl place some warm water, and some mild detergent or a small amount of ammonia
2.   Place your yellow sapphire gemstones in the solution for a few minutes
3.   Remove the jewellery from the bowl and clean gently with the toothbrush using the liquid from the bowl. 
4.   Wash your sapphire under clean warm water until any residue of soap is removed.
5.   Rinse and dry with a clean soft cloth.

 If your yellow sapphire or pukhraj stone is of particularly high quality, it is wise to have it professionally cleaned and examined once every year or so.

Storage
Store your yellow sapphire stones separate from the rest of your jewellery as they can easily scratch other stones and metals or be scratched by any other gemstones in your collection.