The frame should not be the centre of attention, but the item within the frame! A guilded, ornate frame of the family BBQ is probably overkill. Some art always requires glass - e.g. Pastels. Some art must not use glass e.g. Oil paints (this is because an oil painting "breathes"). A mount is optional, but very useful for most items. The exception would be things like oil paints or acrylics. The mount is often slightly larger at the base of the picture e.g. 70mm on the left, top and right, 90mm on the base. The size of the mount is very much personal opinion and does not necessary relate to the size of the picture. Some small pictures for example look very good with large (but light coloured) mounts. Multiple insets in a mount can work very well especially with small photographs or very similar prints. A good example is maps which naturally align. A double mount is required to prevent glass from contacting the framed items. This would be very useful for fragile art like Pastels. Many double mounts will have a strong or dark colour at the back and a lighter neutral colour for the main mount. The mount can often be chosen by selecting a tone or colour from the item being framed. The frame should compliment the style of picture i.e. antique prints / antique style frames and should not be out of disproportion to the item being framed.