What is used to make the bellows black? in Instrument Construction & Repair Posted October 26, 2020 In the US Tandy's Leather Supply is a good source for aniline dyes. Depending on where you are Michael's and other craft stores sometimes carry the common colors. Feibings is a the brand they sell. I used it professionally in the 70s on shoes, purses and belts etc. It is a liquid you put on with a dabber or, in the case of small areas with a brush. It may soak in areas differently and leave the slightly bronze effect Alex West mentioned. If this is the case a top coat like he mentioned would be good. If it were my concertina I'd ask if it were a cosmetic or structural issue. It sounds like you may be dealing with leather wearing away if you are seeing wood underneath the leather. That would imply something more comprehensive than just coloring the spot. (Again, I'm not sure if this is what you are describing.) You might want to post pictures to get the best advice. There are lots of folks on this forum with restoration experience.