I was planning to use an oil-based urethane. How do you apply the wash? Is the first coat pigmented, or do you lay down a coat of pure urethane first?

I apply varnish with a good varnish brush (not foam) and a foam roller with a 1/8 inch nap. I apply the first coat with the brush and tip off any bubbles with the brush. On subsequent coats I apply the varnish with a roller and tip bubbles off with the brush. Coloring will likely look uneven on the first coat or two but that will improve a lot on subsequent coats and shouldn't be an issue. It's not a bad idea to thin the first coat a bit to get better penetration into the nylon. I think the more penetration you can get the less likely the skin will wrinkle due to moisture though I dunno if the effect is significant.

Ken Blanton