You can see perfectly through the X-ray!
Black package. For example, from a printer cartridge.
A great way is a welding mask. I am observing at the moment for the second time in my life, and the second time with the help of a mask. Nothing is visible in it except the sun shaded by the moon.
You can look through an old floppy disk.
The easiest and most affordable way is to pierce a hole with a diameter of 0.2-0.3 mm in the foil, and look through it. Not very clear, but I have now checked - it is quite workable. It is best, of course, to look through filters that cut off not only the visible part of the light, but also the UV spectrum, because without this you can harm the eye. Smoked glass cuts off only the visible part of the light, but transmits UV radiation.
All advice comes down to special devices based on solar filters. All articles on this topic mention that you should NOT look through smoked glass because it does not filter UV and UC, which is harmful to the eyes.
You can look at the eclipse with smoked glass