It is said according to the style of the work. It is usually mounted on thick cardboard before sale (the color of this kind of cardboard may be elegant or gorgeous, and it is also decorated with broken gold foil, the effect is very good). You can buy it back. Place it directly on the frame and hang it indoors for viewing. Because lenses come in various forms and are suitable for modern home decoration, there are painters who specially paint them. These unframed paintings are called mirror centers.