Ron Rider gives some simple tips on how to clean up and restore shell cordovan shoes. Above is a pair of black boots he worked on. The right shoe is what the restored one on the left used to look like. If you want to purchase the various products he mentions in his post, you can buy them from his store.
I love photos like this. It reminds me that if you invest in quality shoes, you can get as much, if not more, from taking care of your shoes as you can from buying new ones.
Also, note that in the comments section, Ron explains what causes those welts on shell cordovan shoes once they’ve gotten wet.