I prefer a whetstone to a "steel" for knife sharpening. Over the years my whetstone has become loaded with steel particles from the knives. As it is basically 13 % chrome stainless steel it is not easy to dissolve. It is immune to nitric acid and hydrochloric is very slow , if at all . Any ideas for cleaning a whetstone ?
If this is an oilstone (which is considered old fashioned exactly because of these issues), an oft-mentioned ultima ratio remedy is boiling it in soapy water. YMMV, this could destroy the stone. If you know what exact type (eg arkansas) your oilstone is, research instructions specific to that stone type.
If it is a waterstone, abrading the stone - with a flattening plate, diamond stone, another waterstone until unaffected material is brought to the surface is the recommended method.
While Bar Keepers Friend is a great cleaner with many uses, it is NOT great enough to clean an ultra-fine whetstone.
I use three grades of whetstone surfaces between two stones to do my sharpening jobs: Coarse, Fine, and Ultra-Fine. Coarse and Fine are on a single bastard stone, and Ultra-fine is a smaller dedicated stone.
The cleaning problem is presented by the ultra-fine whetstone; it remains clogged by particulates and discolored by impurities, the colors of which range from the expected shades of grey to suspicious sticky brown.
Boiling with detergents did not help. Lye (potassium hydroxide or sodium hydroxide) did. Two caveats: Do NOT allow it ANYWHERE near aluminum (it acts as does acid), and use VINEGAR (acetic acid) to neutralize it.
Lye works greatly on lots of things, especially when it comes to deposits involving extremes of heat and time, but it should be used with great care. The reasons why "excessive" bathing was generally regarded as unhealthy was understandable—considering people over a century ago were horribly ignorant regarding chemistry and physics. (nobody thought to bathe with vinegar after applying lye soap)