Hi Aethis,
I have had good luck with use of the cheap, small, steel wire, brushes from Goodwill and other places. They are slightly larger than a toothbrush and look like one. Use pressure along the direction of the grooves and put a couple layers of tape on the scales to protect them because the brush will abrade the scales if they are not protected. If you soak the jimps in MR.Clean or another cleaning agent for a while and do it a few times while brushing it may only take a few minutes to get them clean.

Warning: eye protection is mandatory!! The brush will splatter stuff like mad and the best place to work is in the deep sink of your laundry room!
Have fun!
Respectfully
~Richard