Great exemplar!

Option A:
You can remove the stones from the mount,
put in a saucepan with soapy water and detergent
(powder to water ratio = 1 to 1)
and boil for 2-3 hours, at a temperature
of about 90-95 degrees Celsius, so that there
is no active boiling.

Option B:
Take the oven, heat up to 90-95 degrees Celsius,
take a baking tray and pour sand onto it,
put the stones on the sand and sprinkle around,
how to create a mound.
This is necessary for uniform warm-up. Warm 2-3 hours.

You can repeat several times to clear the stones better,
you can use both methods alternately.

Then the surface can be cleaned with kerosene.