Looks like bone handle scales. I don't think you will improve it by any cleaning other than soapy water and a toothbrush and let it dry quickly. By the way, that style of knife is called an "elephant toe nail" or "sunfish" pattern. They were popular in the early 20th century as heavy duty knives and often used to cut rope. Most American cutlery companies made this pattern and some were made in Germany. Sadly, no amount of cleaning will show who actually made the knife since the makers mark will be rusted away.