DMT D8C lapping plate leaving a gray residue on Norton 4000

I have been having this problem lately where my DMT DIA-SHARP Coarse lapping plate started leaving a gray residue embedded in my Norton 4000. Interestingly enough, the plate is still removing material and lapping the stone. That said, it seems to me like the 4000 is working very poorly with the gray marks. I tried washing the plate with a dish-washing brush and soap to no avail. The DMT plate as been used to lap my stone quite a couple dozen of times so it is far from new.

I made a picture of the stone with the gray residue and also one from the plate. Is there anything I can do to prevent this? .... I heard the Atoma Diamond plates are pretty good at lapping. Maybe I should buy one to replace my funky DMT


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Are you soaking the 4k before lapping and lapping under running water? You are starting to strip the DMT; that's why it's starting to look shiny in places. So I'm thinking either you need more water or maybe you're using too much pressure.

holli4 is right on the money. That gray residue is your diamond plate. Under the tap ...... Running water is a must AFAIC.

+1 here. It looks exactly like that to me as well.

I forgot to mention I am doing it after having soaked the stone and under running water. But I think I have put too much pressure... thanks Holli4

They are the high spots on your DMT that have gone bye bye. I'm not sure but they may continue to leave grey residue as you are now essentially honing the steel on the DMT at those points.

If you decide to go for a new plate the Atoma is supposed to be the cat's whiskers. Way more $ but I hear they are worth it. Haven't gotten one myself as my D8C is still hanging tough.

I have just tried with less pressure and the gray marks are gone. You really have to use the right amount of pressure when using the plate or else debris will stick in it and you will strip it quickly.

Thanks for everyone's help it is really appreciated

I encountered the exact same situation! When I reduced my pressure on the DMT on my Norton 4000, the spots went away. Thanks so much!