The first tip is you can not go too many shades darker with these pigments. You can go one or two shades darker at most. Here you can see what happened when we stained the very light popular floor dark brown. It turned out very patchy and uneven. (Partly this was due to a soft wood and the way poplar absorbs things, but I think it would come out uneven on any type of wood).
We had to go back over the floors and sand part of it off. Then go in by hand and sand the darker bits. It still isn't where I want it to be.
The stairs went a little better as we did not attempt to go too dark there:
Applying the stain is also a difficult procedure. If you just paint it on with a paintbrush or with a cloth it will go on even more blotchy than this, and you will see all the brush lines. or lines from the cloth, because it dries in a few seconds.
Here's how to apply it:
1. Tape off the wood along the seams in 3 or 4 inch sections length-wise. Do not tape it off width-wise or you will have a dark looking seam there.
2. Continually mix the stain/water solution so that you get a consistent amount on the brush. (2 or 3 people are needed)
4. The second person follows, rubs in the stain/removes the excess with a cloth to even it out.
This has to all be done very fast.
A Note on Sealing
On top of the stain we put hemp oil which now I know is not ideal for floors as it picks up grime from feet that can only be cleaned by sanding. The picture on the right is grime from the landing floor. This is just hemp oil with no stain.
You cannot see the grime on the dark floors, but it is there and so it feels less than perfectly clean.
A better sealer for floor and stairs is ECOs clear varnish. It's zero VOC and smells very benign to me.