Watercolours are surprisingly robust but over time when they are not hanging in the most ideal conditions of humidity show signs of foxing. This often makes itself apparent in the sky with a series of unsightly dark spots. This can usually be removed by careful professional cleaning.
I am pleased to discuss with you and give you an estimate on the cleaning of a single watercolour or a whole collection. This might involve just a simple clean replacing the picture in the existing set up or a remount and reframe using the latest conservation materials and special conservation glass. I make a point of always using special conservation glass on all my pictures as it cuts out the harmful ultraviolet light and stop the pictures fading in bright light although I do not recommend you hang your watercolours in direct sun light.