Dear Abraham,

Keep ceramic morter and pestle dipped in dilute HCl for more time and then ultrasonicate it.

For magnetic stirrer, it's coil should not get damaged. So it would be better if you wrap the magnetic stirrer with Aluminium foil always. Hence staining problem can be avoided.

To remove present staining, try acetone.

Thanks.

Dear Abraham Abbey Paul

It depends on the magnetic material. Ferrites, rare earth magnets and high-iron alloys will respond well to HCl (if dilute HCl, as suggested by Anamika Kadam , doesn't cut it try concentrated HCl). Others, such as high-nickel alloys, may require an oxidant, in which case you can (carefully) try aqua regia.

Hey have you tried chromic acid? I use diluted chromic acid for cleaning my glassware, stirrers and also ceramics. Good luck

Dear Sikta Panda

It is best to stay away from highly toxic hexavalent chromium whenever possible. This type of treatment (sulfochromic mixtures in particular) was initially designed in a more safety-ignorant era for hard to dissolve organics, but even for those there are less poisonous options such as sulfuric-peroxide mixture (SPM). While you are not very likely to poison yourself with Cr(VI) in the lab, your toxic waste has to go somewhere...

I recommend to watch the movie "Erin Brockovich". It's a good movie.

Thank you for the information

I sincerely appreciate your kind answers, Sikta Panda Anamika Kadam and Emanuel Cooper they are wonderful. I got it cleaned with HCl as you have rightly suggested.

Thank you very much for the movie you suggested, I'll look it up