We floundered a bit in figuring it out, but here I'll share the things I've figured out. Most of this uses low-odor quick-drying options, because I'm working in a house with small children in wintertime. (They're not home while I'm working, but they need to sleep here at night.)
Tools and Materials:
+ orbital hand sander (or two)
+ plastic drop cloth
+ safety goggles
+ dust masks (buy a multi-pack)
+ ear plugs
+ vinyl-palmed work gloves
+ vinyl or latex disposable gloves
+ cheap throw-away paintbrush for chemical paint stripper
+ paint scraper
+ small wood chisel
+ 2.5" angled natural bristle paintbrush
+ small paint tray
+ 40 grit sanding pads (be sure to get the right size pads with the right number of holes - they're for ventilation and your sander will overheat without the right ones) I used about 15 pads for 14 steps and a landing
+ 40 or 60 grit sandpaper and a sanding block, if desired
+ 2" wide painters tape
+ spool of cotton twine
+ Hi-Speed Ready Strip Citrus Paint & Varnish Remover (this project used one half gallon jug)
+ MinWax Wood Finish (this project uses 2 qt sized cans of golden pecan stain)
+ low-odor mineral spirits
+ MinWax Water Based Polyurethane for Floors (this project uses one gallon of clear satin finish poly)
Here you see the old staircase. Someone had painted that beautiful wood a chocolate brown when the house was built. It was old and dingy and banged up. The dark color robbed the stairwell of all light, making it a dark area even in midday.
Step 1: Stripping the old paint, part 1: chemical stripper
1. Open your windows and turn on a fan. It might be "low-odor and environmentally safe", but it stinks.
2. Shake the bottle really well - it's very separated.
3. Pour some liquid onto the top step. Using a cheap paintbrush, spread over the step in a thick layer. Make sure to get the corners and edges well.
4. Move down the steps to the bottom, and throw away your paintbrush, then find something else to do for about 2 hours. I started the bottom step after a half an hour, and worked my way back up. But during the rest of the paint removal process, the upper stairs that had had the stripper on them for about three hours took a third of the time it took to remove the paint from the lower steps.
5. Using a paint scraper, scrape across the step with the grain of the wood. The old polyurethane comes up with the stripper goo. Wipe the goo off of the scraper, and continue (don't bother trying to rinse it off). I scraped it into an old shoe box, but where doesn't really matter. Scraping takes off most of the stripping agent, I didn't bother to wipe off the remaining.
These steps are old and dinged up, and the dark stain penetrated into the wood, and it's imperfections. I was removing the many layers of old poly with the chemicals in order to get closer to the wood and to get started. The picture here shows the stairs AFTER the chemical stripper was scraped off. It was only the first step of removing the old color, but it made the rest of the project move much more quickly. The time (a day) and cost of the stripper was less than the time and cost of using sanding pads to get through that old poly. Not to mention - much easier on my back. I wore work gloves for all of this step, I really didn't get any on myself.