Thanks to you both for responding. The company is claiming that the pre-existing condition of the wood and the choice of stain is the reason why it is uneven (of course, neither of these things were mentioned to me when I had the guy come out to do the estimate, and I told them upfront I wanted dark brown floors...obviously they were just anxious to get my money.) Greg, I have read some about water popping and may have my 2nd company write the estimate with that in there so that the floors are even darker and more even. I didn't realize when posting that I could only add one photo per post but here is the photo of the sample that was never sanded off before the job begun. You can see clearly here two tiles that are almost black. I am negotiating with the original company now...first they proposed I get another company to do the work and then they will inspect it and if the other company did a better job, they will refund me my deposit ($900)...yeah right. What a joke. And did I mention this is a small 1 br condo and I have been completely displaced from my apartment by the work - my kitchen and bathroom are filled with my furniture! What a headache.

Okay okay, you're forcing me to tell the other kitchen story. Love that one about the Mercedes---best not to touch the leather or something?? Sometimes I feel like Indiana Jones in this house, making archeological discoveries and not so much un-remuddling. Thought I had a very very ugly wall and base cabinet combo with a cheapy formica countertop, so I decided to tear out the wall cab and have this new window installed there instead. South exposure is very important in Mpls. Was tearing out the cabinet prior to window guy arriving and realized, to my horror, that this was a built in that had been bastardized by someone's application of wood-grain plastic laminate. They'd removed the doors (sob), stuck dark wood laminate on all the surfaces, and installed MDF doors. No wonder it was so difficult to remove? Had I known, I probably would have kept it, but as it was chewed up by my removal efforts, I kept the base and am painfully taking down the glue goo and tossed the ugly doors, etc etc. These people apparently liked the *look* of wood, but preferred it in its plastic form. *sigh* Thanks again lads, appreciate it. Will be trying SoyGel first. We'll get her back to her full glory, poor thing.

That worked great and didn’t turn the floor green like the baking soda solution I tried first. Thanks!

I have to agree that these were preexisting but almost invisible because of the sanding. The top pic looks like "old finish" was left in place. Considering how thin your boards are and how old they are, this is not unexpected. And to be clear, old floors can have 80 years worth of contamination (ie. wax, shoe polish, Pledge, Murphy's Oil soap, soap, hairspray, hair dye, etc) on them. These products can, and will, get past the original finish and contaminate the wood. Just like old urine stains pushing all the way through a board (the dark gray stain is most like an old urine stain...cause that's what they look like after many years), these contaminants can go several millimeters into the wood. Especially things like cooking oil, Murphy's Oil soap (anything oil based really) or even melted wax from a candle. After sanding, you wouldn't have 'seen' these things. But a quick swish of a slightly damp mop (make it wet to give some depth of colour) and all of these things would have been evident within moments of the water touching the wood. And that's why you can see them now. The clear coat is like water hitting the wood. It gives the colours depth...and definition. But unlike water, the finish is permanent. At this point, I would keep going with your plan = 2 more coats of Loba 2K Invisible. And You will want to hurry. To get a good 'stick' the next coat should be put down within 24 hours of the previous...or else the flooring guy has to abrade the floor again to get a mechanical grip rather than a chemical stick. Keep going. Know that you are getting 20 years more out of these floors that probably should have given up the ghost 20 years ago. That means you are extending the life by 40 years. For an old hardwood floor, that's impressive.