Film from the patch
She has two sides: smooth and matte. On the smooth side, the drop will spread, since there is nothing to catch on it. As a result, it comes into contact with air over a sufficiently large area, dries quickly, and the working drop loses its properties. It is better to use the matte side of such a film since it has a rough surface which prevents the drop from spreading. A working drop is formed from above in the middle and retains its properties for much longer.