Using Welding Glass As An ND Filter

I've been trying to use a piece of welding glass as a filter for my camera. This is an Update; I found that the best way to attach it to my camera is probably to tape it onto an existing filter such as a UV or PL. I also found that it's practically impossible to avoid vignetting. It's practically impossible to get rid of the color cost in post post processing using Photoshop Elements 15 and/or GIMP. To keep vignetting to a minimum, I had to apply tape right on the edges so that it was barely holding. That's not good because that way, I risk light leaks that can cause internal reflections. I zoomed in on the image 100% and I can't notice any reduction of image quality. It would have worked out better with a square piece of glass, but I think I'll just opt for a regular filter. so that I can achieve 15 second or so exposures in midday lighting.