What is the knocker for?

The batten is the internal part of the frame, or the depth that is created between the front part (the one we see) and the back part (the one that rests on the wall). Depending on the depth of the batten, frames are distinguished with a low batten (ideal for prints and photos on paper), medium and high (suitable for thick works or to support a double passepartout).

The swing allows you to create a distance between the artwork (or photo) and the glass
protective. This is particularly important to prevent the work from adhering to the glass and being damaged by humidity or temperature changes.
Thickness of the work: The door must be deep enough to accommodate works of
different thickness, such as paintings on a frame or prints on cardboard. There are frames with different heights of battens. Frames with higher battens are usually used for works with passepartout.