I work with lots of old wood finishes (most recently, matching new and old finishes on a 1922 Rolls-Royce, boat-tail, designed by Olin Stephens). First, do no harm. Find a representative grain and color on the existing cabinetry that isn't easily seen. This could be the underside of a drawer lip, an obscure corner, you get the picture. Start first with a white cotton towel or rag, dipped in denatured alcohol. Gently rub a small section of the oiled wood, in the direction of the grain, then let it dry. Look at it very carefully, under strong lighting
. Also notice what came off onto the white rag. If this works for you, then try it GENTLY on a whole object, such as a drawer face or back of a cabinet door. Still okay? Move on to a whole cabinet. What you are trying to do is damage as little as possible should you screw up.
Now, say you are successful, but you want it even lighter. Try repeating the first trick. If that doesn't really do it for you, move to the next phase. 3M makes a variety of rubbing pads, in different levels of scouring ability. Get a fine pad and gently rub the wood, again, in the direction of the grain, then wipe with the cotton rag. You will now be moving into the mechanical removal
phase of cleaning
old finish. Be VERY careful about skipping too quickly up to heavier grades of abrasive pads, you can do real damage if you aren't careful.
Now, you are at the stage where the color is just about right. The problem is that you have discovered why cabinetmakers use dark stains and oils - to make up for the lack of uniformity in different woods accepting stain. If some of your wood is mottled, or completely different than others, you have to play the same game
in reverse. Fortunately, it's a simple matter of doing what you had been doing for years.
Pick an oil
you feel good about using on the boat. Oil
all of the wood with the same stuff. Now, for the lighter bits, you have to make a custom stained oil. You will have to look at the color in a strong, white (daylight or 5000K flourescent). The color may need one or two key colors, besides the obvious brown. A professional furniture finish supplier (look under antique repair suppliers) will be able to provide you with very small amounts of various colors (we're talking drops here, not pints). Add the colors to sample jars of your regular oil and apply them. If they don't work, remove them with the alcohol.
It's a pain, but it works and doesn't ruin the cabinets.