Accidents happen. A case of (literal) butterfingers could make you lose grip on your recipe box and ding the edge of the kitchen table. A perfectly respectable man can inadvertently drop one of the kitchen chairs while moving it up to the bedroom. Maybe you came in from the garage carrying a cinder block and needed to set it down quickly, not realizing until you picked it up again that in doing so you laid it on the end of the dog's leash, and now your wood floor has the perfect impression of a snap swivel right in front of the coat closet.
One approach to such mishaps is to say “Thank you! My furniture (or house) now has more patina!” Your wabi-sabi outlook on life might lead you to take this attitude, and if so that's fine. I go that way myself, quite often.
But right now, I'm making a chair, and it hasn't even had a chance to be a new chair yet, so I was dismayed to take the rear legs out of the bending jig after I steam-bent them to see this:
How did this happen? The bending jig is made of yellow pine, and its grain embossed itself onto the chair legs while they were clamped into the jig. Soon you will see a post on “Appropriate Bending Jig Materials” perhaps . . . meantime, I don't want to make two new chair legs. What to do? Bondo? That's a lot of work, and I didn't plan on painting this chair.
So I borrowed a clothes iron, got a clean rag sopping wet, and pressed the rag into the dent with the hot iron:
It took a few minutes of effort; I probably put the rag onto the wood and hit it with the iron about 5 times in as many minutes. But here's the final result:
Not too bad. Not perfect, but no longer a glaring flaw in the finished chair.
So, some explanation. When something hard hits wood, two kinds of damage can happen. The wood can be compressed, or wood fibers can be torn/broken/severed. Fairly often both happen in the same event. For instance, lay a house key on a pine board, teeth down, and hit the back edge with a hammer, and you'll get both tearing and compression. Also a restraining order in certain circumstances.
Quickly introducing water, as steam, swells the compressed wood back to a normal or near-normal size. Obviously, adding water won't rejoin the ends of severed fibers, but this trick minimizes the appearance of the damage.
Of course you'd rather do this on unfinished wood. I give no warrantee as to the effect of this treatment on paint, stain, varnish or other finishes. Having said that, though, I can tell you it works fairly often without damaging the finish, the older the finish the better. As always, test in a hidden area first to be sure!
Real expert guys say to use not just a clean rag but a colorfast one. The red shop rags you got at Auto Zone will turn the wood pink, even if you've washed them three times. Real picky types say to use distilled water, to prevent mineral staining. I wasn't worried about that here, because as you might notice we've already got some slight iron staining going on in this chair, and I plan to ebonize it later. I haven't ever had an issue with discoloration from tap water, but I haven't done this in all 50 states, either.
Finally: this principle has been used to make wooden sake boxes leakproof. If you think about it a while, I think you'll see how.