I had taken all the reeds out while replacing the valves, so I decided to give them all a light clean before putting them back. First I used a fibreglass pencil to clean the top of the tongue and frame, then I washed them in a mild degreasing solvent (panel wipe), then after they had dried I wiped the undersides of the tongues by sliding a piece of paper under them, before finally dusting them off with a fine paintbrush and examining them closely under a bright light.
Before and after cleaning:
Here's an interesting thing I spotted. The reed frames are all stamped with their note value, as you can see in the first picture. Is this reed a D# or an Eb? (I think it is actually in a D# position, though the two notes are enharmonic anyway.)
I also took the opportunity to adjust some of the tongues that weren't speaking nicely. Here are the two reed boards finished (for now) with new valves and cleaned/adjusted reeds:
Incidentally here's the "bellows bench" I built so I could test the reeds outside the instrument. It clamps to the bench and screws onto one end of the concertina's bellows in place of the usual end. A professional concertina repairer/maker would typically have a spare set of bellows dedicated to this purpose. The thing in the middle is an adjustable hard-leather tapered shoe that the reeds slide into. The thing on the right is a valve that lets air out when you lift the bellows (the bench only operates in the 'pull' direction). The yellow string is to make sure the the bellows don't open too far.
A dovetail-shaped reed in the shoe of the bellows bench. This is one of the largest (lowest) reeds there are in the concertina. Leather proved a good material to make the shoe from because it is slightly flexible. My first attempt was made from thin plywood and I wasn't able to make it fit every size of reed without leaking.
Rather blurry photo of the reed playing a note.
This was an experiment that failed in a rather interesting way. When I first built the bellows bench, the slot under the shoe was simply open to the inside of the bellows, and it worked fine but I thought perhaps the lack of any constriction was causing the large reeds to use too much air. It also occurred to me that it might be very useful to be able to rapidly turn the air on and off like you can in the real instrument so you can observe how quickly the reed starts to oscillate after the key is pressed. So I knocked up this contraption on the underside of the board:
The result was very interesting. The high and low notes behaved exactly as before. The middle notes wouldn't sound at all. They just hissed a little without oscillating, regardless of how much or little pressure I applied to the bellows. Occasionally I would get a quiet squeak at some high multiple of the correct tone. It wasn't lack of air flow causing the problem because the large reeds played just as well as before. I tried both ramping up the pressure very slowly, and applying pressure with the pad closed and opening it quickly to cause a rapid pressure rise. The only thing that sometimes worked was sliding the reed half-way out of the shoe so that some air could leak past it. After removing the contraption the reeds all worked fine again. I think there must have been something about the size of the chamber formed underneath the reed that prevented certain frequencies of reed from oscillating. It was lucky I only tried adding the contraption after I had successfully used the bench with all the reeds without it, or it might have taken me a long time to figure out what was causing the mid-range reeds to not sound on the bench. I have a couple of ideas of other ways I might be able to get it to work but I haven't played around with it any more yet.
Time spent cleaning and adjusting the reeds (not including making and playing around with the bellows bench): about twelve hours. Though I also recorded the error of each reed on the bellows bench while I was adjusting them, which probably accounted for at least an hour of that time.