Maps have often been dry mounted or glued to another surface. This can often reduce value a great deal as the glue or backing can contain substances that make the map susceptible to wear, discolouration or other deterioration. A skilled paper conservator can often remove the map and reduce the side affects. Sometime folded maps have deteriorated to such an extent that they are professionally rebacked with tissue or rice paper. This usually enhances value compared to a map that needs restoration.
Colouring varies with old maps.
When they were produced some maps were fully coloured at the time, some were partly coloured, some were coloured in outline, and many not coloured at all. When maps were coloured at or close to the time of production it is referred to as contemporary colour as it is contemporary to the printing of the map. Maps were originally coloured to enhance appearance and readability. Often older maps issued without colour have colour added in whole or in part. Any colour added long after the map was issued is referred to as modern colour.