Traditionally, linen liners have been used in this way:
They are used on canvas paintings (oil or acrylic) with no glass. The liner separates the art from the frame, just as a mat would do in a situation that requires glazing.
But here in this 21st C, I am seeing less liners on canvases for a more modern look. (See floating frames and gallery wraps, but also frames are going directly onto canvases now.)
But then recently, Jonathan Adler gave the world vibrant linen liners. (Below, on right)
Immediately, I saw how they could be used on kids art:
In the examples above, they are used like a mat, but are narrower than a mat would typically be. (Mats are usually 2 - 4" wide.) These liners are a mere 3/4" inch, which is great in the case of these vibrant colors, because any more would distract from the art.
Below is an awesome project with more grown-up art:
This is an original promo card from the musical HAIR c. 1968, a cherished memento belonging to an actor who would later perform in a production of it.
Below, you can see these liners work beautifully with watercolors as well.
And below here, an original gouache. (Love that gray liner! True, it's not as vibrant as the other colors, but works so well with black & white art--it makes for an easy transition to any frame, like the hammered pewter-look one here.)
And then some clever interior designer and I figured out these liners could be used inside the vivid metal frames from Nielsen. Look out world! Below, a bright blue liner in shimmering blue metal frame for the Queen.
And below here is a bright red liner in a shimmering pink metal frame to highlight the colors of the mural in the photo.
In every instance above, the liners are used with glazing, and usually in place of a mat. I love that this traditional framing material is in unconventional colors used in non-traditional ways.