Most people do not realise when it comes to framing, that it is essential to have a mount surrounding whatever is being framed. There are a number of reasons for this but typically the mount is used to attract the eye towards the artwork and also help preserve it.
The width of the mount that you are using is very important. Having a mount that is too narrow is distracting to the eye and will prevent your art from being shown off correctly. The mount should be of a reasonable width. If you are unsure about the size of width you should be using, then speak to your framer who will be able to advise you about what would be the best size to use. They will also advise you about the colour of mount that you should be using.
In terms of preservation, the mount acts as a separator between the artwork and the glass. It is important to have a small gap between the art and the glass because if there was no air gap, moisture would turn into condensation which could eventually lead to mildew and mold being present on your artwork.