I am talking years of grimey oil which has discoloured them. A soak in washing up liquid hasn’t cleared even the surface gunk. A soak in bleach next? Cheers

Road Traffic Film remover will do it.

Only downside is you have to buy it in 5 gallon drums.

I use mine for all sorts of things other than the obvious car cleaning.

If you are local to Staffs i’ll let you have some.

Cillitbang

Bang! I’ll try it.

Thanks, curvature, but I’m up in Scotchland

Disc brake cleaner or degreaser and a good rub with a clean cloth.

Try Dot 5.1 😀

Flash and a scrubbing brush

They look lovely in a “look at my new bike” thread, but, in reality you cannot beat black grips.
I had a set of specialized grips actually post themselves by air mail to get away from the handlebars.

White Spirit and a toothbrush.

Rhino Goo cleaner, very impressed how well it cleaned my minging white saddle, so should do the business on grips.