Getting ready for the solar eclipse… I bought some 0.2mm silver mylar, which is practically opaque, but lets a tiny bit of sunlight through (like, about 1/160,000th by my seat-of-the-pants estimate). One layer of it makes the sun seem about as bright as the moon. Two layers, and you can’t even see the sun at all.
THIS MAY NOT ACTUALLY BE SAFE AT ALL. I don’t honestly know, because I have no way of knowing how much UV light gets through this stuff. But I did use mylar to look at the last solar eclipse several years ago, and I haven’t gone blind yet, so there’s anecdotal evidence at least.
Here’s a good article explaining when and where you can see the eclipse. If you’re in the San Francisco Bay Area, it should start on Sunday afternoon (May 20th) around 5:30pm, and reach maximum occlusion (about 90%) by 6:30pm.