You've not cut yourself deeply with a razor til you've cut yourself with a cut-throat straight razor. I stupidly last year went to catch my razor after it fell off the side of the sink as I was lathering myself up with more soap. I say stupidly as my blade was exposed so I should have jumped back and let it go. Sure enough I reaction caught my razor in mid air, snagging it by the blade end. I got cuts across the inner part of the top knuckle on 3 fingers... how deep were the cuts? Oh, only to the bone. Thankfully, I was able to seal the cuts by using pressure then a spray plaster (these are the bomb for cuts, it literally feels like you've got a can of synth skin from a Sci-fi when you use them) but every time I flexed my fingers out I'd rip them back open for the first few days.

Using duct tape to cover a wound isn't as dumb as it first sounds. Your primary objective is to keep the cut clean which in a mechanics shop can be pretty difficult. Duct Tape is a waterproof seal. As such, putting a bandage and normal plaster on a wound then covering that in duct tape temporarily if your hands are likely to get very dirty or become exposed to dangerous liquids wouldn't be such a bad idea. I'd advise against it long term however, as the wound will not breathe and that will slow the healing process.