Seppi, unfortunately, there is little you could do with the blade. The only thing that could be done is to abrade it with something such as sandpaper, emery cloth, etc. Even then, you would have to work carefully around the inscription, motto and maker's mark. After all that work, the blade would still look like a mess, maybe even worse than it does now. It would be impossible to polish between the lettering and have it look right, at least by conventional means. If I owned it, I would leave it as is, as a relic.