Why does oil reduce the effectiveness of Japanese waterstones?

I've read in several places that oil should not be used on Japanese waterstones, but none of the sources explain the reasoning behind this. What, if any, damage would using oil cause and would it be reparable?

sharpening

Best Answer

Japanese style whetstones made of natural material, also known as "waterstones", rely on water to make a paste from the material, and this paste is abrasive and aids in sharpening. Oil is not as effective as water in making this "mud" as the stone material isn't as soluble in oil.

Further, once you have used oil on any type of whetstone, water may no longer be used as a lubricant, as it will be shed by the oil that has soaked into the stone and be ineffective in carrying away the swarf (metal abraded from the blade by sharpening).

Here is a FAQ on natural waterstones from an online retailer.

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Does oil ruin a whetstone?

Oil is viscous, does not evaporate, and can harden into a varnish. From the sound of it, Japanese waterstones, are soft and large-pored; just the sort of thing a metal powder loaded semi-drying oil could soak into, polymerize and ruin.

Can you use oil on a Waterstone?

According to waterstone manufacturer Norton, you shouldn't use oil on waterstones because the oil will clog the stone's pores. That would keep slurry from developing. Slurry is a soupy mixture of water and loose abrasive particles, and it's what does the honing.

Is oil or water better for sharpening stone?

Overall, the oil stones showed the greatest difference between wet and dry use, with the dry being much less efficient. In each case, the stones used dry required cleaning or resurfacing after the test, but the stones used with oil did not. Coarse Crystolon stones were used for the test.

What kind of oil do you use on a whetstone?

Mineral oil is an ideal candidate for sharpening because it is light and does not harden or go rancid. A light oil is desirable because a heavy or viscous oil will interfere with the sharpening action of the stone.

Tips for Waterstones

Sources: Stack Exchange - This article follows the attribution requirements of Stack Exchange and is licensed under CC BY-SA 3.0.

Images: Karolina Grabowska, Dids, Dids, Teona Swift