This video gives information of blowing shankh .
There is layer of algae on shankh called as skin, if animal in shankh dies and shankh is filled with sand then the skin goes away and looks white , if shankh stays below sand for long period it will have small holes on shankh.
Generally shankh is done grinding, polishing and cleaned to look attractive and white.
please don't ask for purchase of gaumukhi shankh ( Panchajanya ) and big size panchamukhi shankh with thorns , these are on verge of extinction and banned by Indian government , these shankhs in video are shown for demonstration purposes only