Likely non-boiled linseed oil, aka has had no driers added, will harden but can take years. Most common military wood finish gave decent protection, cheap because it was a by-product of the linen industry. Stocks were put in a vat of it that was hot for a hour or so. (AKA it wasn't boiled, adding the metallic driers required it being boiled, hence the names.) Boiled is what us that use it for finish use, with a lot of work boiled is the prettiest walnut finish out there. Takes one or two months to do it right do most people use Tung or others.