I wanted a harmonica for a long time. When I was 9 or 10 years old, I bought a harmonica by mail order, sending away an envelope full of Bazooka Joe comics and a dollar or two. At that price, I had no reason to believe Bazooka would send anything other than a toy. Imagine my surprise when I opened the box to find a genuine Hohner Marine Band harmonica! Somehow, by the end of that day I had managed to lose it. Recently I wondered, could I get another just like it? The answer, thanks to eBay, was yes.
Playing a second-hand harmonica is probably more hygienic than borrowing you buddy's toothbrush, but not by much. Thankfully, several crafty people have written helpful instructions for harmonica disassembly and cleaning. I followed the Instructable by tiltmonkey, and have had very good results with each of the three I've done. This post paraphrases the process. The photos are of a harmonica that I cleaned for a friend.
The first step is to very carefully disassemble the harmonica. The outer covers look like they're screwed down (photo 1), but those aren't screws--they're tiny nails with slotted heads. You can use a knife blade to gently, gently pry off the covers.
The harmonica turns out to be a wood and brass sandwich. The comb at the center is, according to Hohner, made of pear wood. Ten reeds are riveted to each of two brass reed plates that are nailed to the comb, with the chrome plated covers protecting the reeds. Everything has to be handled carefully to avoid damage. The heads can pull off the nails, the reeds can be easily bent, and the comb can split.
The reed plates can be cleaned in soap and water, vinegar (to remove corrosion), and alcohol (to remove remaining bacteria).
The comb can be sanded with fine-grit sandpaper laid on a smooth planar surface, like a kitchen countertop. I was cleaning two at once--my friend's harmonica is the one that does NOT have a split comb.
These photos were taken before sanding, when you could still see the saw marks in the wood.
The next step was the most interesting: sealing the comb in a heated mixture of bee's wax and petroleum jelly. You dip the comb in the liquid wax for a moment, and the wood soaks it up. This process turns the pear wood a beautiful darker shade.
For sticking a harmonica back together, try needle-nose pliers, but be very careful again with every piece. And be sure you get the reed plates on in their correct orientation.