My Naniwa Synthetic Stones Need Cleaning Can Someone Tell Me How?

I have a set of Naniwa synthetic stones that I use. I've noticed that they have gotten dirty over time and I can't seem to clean this stuff off. Old swarf, I think? I always clean my stones with water and I have tried just an ordinary scrub pad with warm water and soap but no luck.
I'm wondering if a lapping stone maybe?
I do have a fine and a course DMT diamond honing stone that I use for my knife sharpening. Could I use one of those as a lapping stone?
I would be grateful for any help or suggestions.
Thanks all.
Chris
https://i.imgur.com/IYhrCrR.jpg

You certainly can use your diamond bench hones for lapping and cleaning these. There is a slight difference in my mind between those two activities. Cleaning them is a quick couple of laps with the home and the diamond plate together to help keep it true and clean. Lapping involvements a grid pattern and checking to ensure its flat and straight. I clean my hones regularly during honing sessions. I think clean cuts the best. I’m not trying to burnish them. It shouldn’t take you long to get those pristine.

Thanks Shaun, I will do just that!

It depends on the grit and softness of the stones, but a coarse DMT generally works well with clearing off swarf. In the short term, while honing, and under a lightly-running spigot, I will run my forefinger on the surface of the stone from time to time to lift off any swarf as it accumulates. But at some point, things do build up and it's time to resurface it.

There are also some dedicated swarf cleaning stones out there, or one can cut a piece off one end of the stone with a hacksaw or tile cutter to use it as a cleaning stone. This, to me, is more about cleaning whereas the lapping plate method (more common) is more about lapping and possibly uses up more material.

Diamond plate, carborundum stone. They all work.

Thanks gentlemen! That worked awesome.
Better than Jack the Bear. All cleaned up and ready for next hone.

I have found that Scotchbrite pads, especially the coarser brown and green pads, do a pretty good job of cleaning swarf off stones. However, if you overdo it, you can mess up the flatness of the hone.

If you have a series of Naniwa hones, you can always use the lower grit hones to clean and flatten the higher grit hones and then work your way down through the series. However, you have to have some other way of flattening your coarsest Naniwa. SIC sandpaper or SIC powder on flat glass or granite will work.

Thank you for all the help and suggestions folks! Much appreciated.