Watercolours should always be over mounted to lead the eye into the subject matter. Watercolours are best framed using conservation or museum standard materials as the lower acid contents or neutral pH levels of these materials help to preserve the watercolour's subtle colours. Higher rated Ultra Violet light filtration glass or museum glass can also be useful for helping to preserve the colours of watercolours.
The best results are sometimes achieved with double over mounts which also create more of a three dimensional effect leading the viewer's eye into the picture. Using more than one colour mount ensures that more than one colour section of the watercolour is emphasised. However sometimes a simple, neutral, off-white mount will work just as well. The overmount could also have watercolour wash / line decoration added to match the tones of the watercolour painting itself. The watercolour should always be framed with neutral pH backing as well as a barrier board between the watercolour and the backing board.