Any professional framer will tell you that any painting or picture should be mounted before it is framed. This is primarily to separate the painting or picture from the glass and prevent the glass from damaging the artwork. Glass easily sticks to paintings, photographs and prints and it can ruin a good picture if you aren’t careful. It is these little attentions to detail that you need to take care with when you are framing and mounting your artwork.
If your painting doesn’t suit having a mount for whatever reason, there are framer spacers that can be inserted into the frame to prevent the glass from touching the artwork. Most pieces of artwork however do look fantastic when they are inside a frame with a mount.
A professional framer will be able to give you this sort of advice when you have your artwork professional framed. Although it may seem cheaper doing it yourself, you will not get the same quality or finish that you would get from a professional framer. Their frames are built to last and in some cases can be made to order so your frame is totally unique for your artwork.