I have "made" driftwood several times. What I do is go out to a wooded area and look for fallen solid logs, (ones that the termites have not bored into) that are hardwoods. I then take a screwdriver and peel most to all of the bark off. After that I rinse it in the tub and let it set for a day. Then I let it dry and then bake it in the oven for about half an hour on 100 degrees. I repeat this about 5 times. After all of this is done I place it in a NEW tank with only plants, weight it down and let it cycle. While it is cycling a white slime tends to grow on the log and snails that I let hitch hike on the plants eat the slime and softer outer part of the log. After the tank is done cycling, which tends to take longer IME, I then run carbon to get rid of the tannins and then the rest is by the book. So all in all it takes a lot longer to make it yourself and it is possible to throw your tank into the nether regions of chemical imbalanced doom, but if you are poor or find the coolest piece of wood ever, this may work you.
Words of Wisdom: Don't gouge yourself with the screwdriver, watch the log when it is in the oven, don't use a pine log, you could probably do this in a older tank but don't bet your fishes lives on it, and shrimp really like the slime that grows on the log too. I hope this dissertation helps but is really a lot easier to just buy the driftwood