Join Date: Jan 2016
Location: Boulder Creek, CA.
Do not oil or WD40 old leather. IF you WD40 the leather you will never get rid of the odor and any thing like mineral spirits or vegetable oil can crack old leather as it dries back out, as can WD40 (turns it brittle).
What has likely happened is that there is a ferric-oxide-tannic-acid complex that has formed through corrosive action between the leather and the iron present in the blade. This creates a pretty darn close and firm surface adhesion of the two materials.
My recommendation (as a leather worker) would be to re-hydrate the old leather with a dilution of glycerol. This will bloat it slightly (breaking the bond) and make it a little more flexible. It will also extend the life of the leather. If it won't come loose after a few hours of soaking. it should still be softened enough to safely peel back.
So at that point you would want to find and carefully snip the stitching. Good to save the stitching material and take well focused close up pics before hand and as you go along. That way you can figure your way back to restitching it correctly.
But before putting it all back together I'd scrub the inside and use an animal glue to adhere naturally processed light canvas weight linen fabric to the inside. alternatively rubbing the inside with beeswax can lay down a more temporary protective barrier.
As for cleaning metal. Wood ash works wonders on brass, bronze, pewter, and silver. For iron, steel, and nickle use cream of tartar (both of these being made into a paste by mixing with water). Wool roving and natural sponge I've found make the best scrub pads.
It's also always a good idea to cleanse metal at the end before oiling. This is done with a 2:1 mixture of baking soda and powder non-iodized salt. The blade is wetted with water and coated in the powder. White vinegar is then drizzled lightly over it causing it to foam up. This will lift any deep grime from the surface and float it away. Immediately after you want to rub thoroughly with more un-mixed baking soda to neutralize any remaining acid. Then wipe clean with a soft cotton cloth and non bristled pipe cleaners (to get in those cracks. After which you can oil as normal.