Here is another example of how soaking some bone scales in oil can cause very dark staining
Here are more knives that have evidence of oil soaking in unevenly.
On the left is a Russell I immersed in mineral oil, notice how there is a large area of darker color to half the handle. That portion of the bone became softer, and gouged easily when I used a buffing wheel on it.
Next is a "restored" Keen Kutter I got off ebay, notice the extra dark bone along the backspring edge, at the middle pin, and elsewhere
Next is a Boker with porous second cut stag handle, notice the dark spots in the middle of the handle where I put 3 drops of mineral oil that soaked into the pores
the "damage" caused by soaking in oil is that the oil changes the color of the bone unevenly. It tends to go in around the pins and under the edges of the scales, more than on other parts. Not all bone handles react the same way, as the density of the bone varies from knife to knife.
Even the two sides of the same knife react differently, for example, the Pile side on the Keen Kutter has much more oil staining than the Mark side
In the following photo, the Remington on the right shows just a very slight shadow where oil soaked in more than other parts of the bone, on the backspring side between the middle pin and the bolster. It left me with the impression that Remington bone is denser than the bone Russell used. The Charlow on the left showed very little change from oiling. Bone density varies a lot, and some cutleries use higher density bone than others. Gecs Primitive bone is so porous, that they stabilize the material by soaking in acrylic. After which oil will not penetrate at all.
In this next photo you can see that the Mark side of the Russell absorbed much less oil than the pile side, mostly only around the pins.
I do recommend using mineral oil for the pivot pin and blade of a carbon steel knife. I just no longer soak my handles with it.