High archival potential describes the ability of photo paper to preserve a printed photograph in its original form for many years, often decades. Such papers are made to resist common signs of ageing such as colour fading, yellowing or embrittlement of the paper substrate itself. This is achieved by using materials that are free of acids and other substances that cause gradual degradation. The paper is often supplemented with protective layers to protect it from external influences such as UV radiation or airborne gases. A photograph printed on such paper retains its colour and quality even when stored in an album or displayed indoors for a long time. The resulting durability is always a combination of the characteristics of the paper, the inks used and the storage conditions, especially protection from direct sunlight.