An awful lot depends on what type of finish is on the wood. The link below lists some ways you can use to tell what finish you have. You need to scroll down a bit to find the info. Here is a link that might be useful: how to determine the finish

Thanks! I appreciate the suggestion of the thinner. I hadn't thought of that. It is not unfortunately natural variation in the wood-I think sombreuil hit the nail on the head about too much wet mopping. Oil certainly could be holding dirt-but then wouldn't I be able to get the dirt off? I have tried everything. I did sand a small spot in the pantry and it did seem to come off with sanding, so it's not the wood. Thanks again! I would have come back sooner but I didn't get the notifications that I had replies so I thought no one had any ideas. Appreciate it!

As JLC said, you have nicely finished doorways ... the only time you will see both floors is when you have a door open. And with the difference in lighting, you won't notice slight differences. Here's how I match or blend finishes: Bring home some samples of the prefinished you are thinking about and lay them in the hallway, parallel to the existing floors. Stand back 10 or so feet and pick the board or boards that you have the hardest time spotting. That's your match. Or, remove the boards that stand out ... what's left is the matching color. If you carefully pick the ONE board that is just inside the doorway to be as close a match to the older one in the hall it will make the blend almost invisible. Here, in an 1880s adobe ... the door stops where the pale wood is, and I picked new boards with the brownish tones of the old floor (upper part) to make the new flooring (running side to side) less conspicuous. (there was craptastical 1990s carpet and some wierd sill arrangement to deal with ... nothing in the house is square, plumb, or level). By matching size and rustic-ness in the new flooring we got a floor that blends with the old. Cleaning and refinishing the old floor (eventually) will make oit blend better.

Those are all good and valid points. To clarify any confusion, solid pre-finished hardwood floors can be refinished if you ever need them to be. Theres a bit more sanding involved to get the factory finish off, but it's done all the time. The floors get sanded down, and the bevels are no longer there, leaving you with a newly site-finished floor. The little grooved edges are called micro-bevels, and the durability of your flooring greatly depends on its installation. Those microlevels won't necessarily cause your flooring to be more susceptible to water damage than a site finished floor, as long as the installation is nice and tight. Yes, your hardwood floors will expand and contract, but every wood does this. It's just a natural characteristic. Quartersawn hardwood is known to have less movement than plain sawn, so if the gaps are a concern, you may want to think about looking into quarter sawn hardwood. Having hardwood in a kitchen is risky regardless if it's prefinished or site-finished. You just need to know, as a homeowner, that certain precautions need to be put into place to ensure the longevity of your floors. (Especially in a kitchen) Another thing I wanted to touch on was the fact that you said you had carpet in an area and tile in another. This would mean (hopefully) that the tile is sitting on either cement board on top of plywood, or there is a cement subfloor where the tile is located. This would have to be addressed when the tile is removed, and you are probably going to need some subfloor prep for your hardwood floors. Most likely additional plywood to bring the elevations of the floors to the same height. Many factory finishes are, in fact, more durable wear layers than a site-finished polyurethane coatings. And that is one of the reasons why many pet owners choose pre-finished floors. As long as you're not choosing a particularly soft wood, a prefinished floor would be just fine for your home. It would make sense, having children and a pet because of the time you'd have to vacate for the finishing process of site-finished floors. It would, overall, be an easier install. The quality and longevity of your hardwood floors depend on the quality of your subfloor, and the quality of the installation, not whether you have site-finished or pre-finished material. Good Luck! Pre-finished vs Site-Finished Hardwood floors