Originally Posted by Fabienne
Here's the answer from a friend of mine
Fabienne, my guess is that the smell comes from the quality of the tanning process. The tannery uses chemicals, including salt, to remove hair, etc. and then extracts of tree bark (tannin) are used to strengthen and color the leather. If this process isn't done well, the leather still maintains some of its flesh-like characteristics and can slowly rot, just like flesh (yuk!) It may also be that the chemicals were not well removed at the end of the process. I suppose that you could try baking it in a low temperature oven (say 200F) a few hours to kill any microbes, (or drive off any remaining volatile chemicals) and then give it a good coat of mink or neatsfoot oil.
I think that your friend's explanation is most unlikely, and a fishy smell is not characteristic of rotting leather/flesh. Rawhide is untanned leather, and it does not produce these smells.
Oil tanning was the traditional technique to produce chamois and other soft leathers, but I suspect that the odour has been produced by one of the oils used in finishing the leather after it was dyed. I think that putting the belt in an oven would be rather drastic. I would wash it with a good quality leather soap, and use a beeswax leather finish to disguise the smell. Many people find the smell of neatsfoot oil unpleasant.
It may be worthwhile speaking to a saddlery for advice.