Antiques are often defined as collectibles over a century old, which show qualities such as rarity, good condition, beauty, quality, craftsmanship etc. Whilst items such as furniture and art conventionally are 100 years or older, cars are the exception to this rule; in the US, an antique car can be a mere 20 years old, whilst in the UK a vehicle must have been built at least 45 years ago to qualify for this title. Although most antiques have some element of rarity about them, some are far less common than others. Rarity can be caused by numerous factors, from systematic destruction to limited production. The uniqueness of an item can also be determined by the owner of a piece, with celebrity or royal ownership often increasing value and desirability. A design which diverges from the characteristic style of a notable manufacturer, designer or artist can also affect the rarity of a piece.