Spotted this elsewhere. A newbie was being given advice to use sifted sand/dirt of the desired colors for one's scenery requirements, as long as it was heated in an oven on low heat to kill bacteria, etc. This was good advice as far as it went. I must also add that it is very important to run a big MAGNET thru all the stuff you collect. An old radio speaker works great, as the magnets on speakers are usually very powerful. By doing this, you remove all ferrous debris and prevent the motor magnets in your locos from attracting the stuff, which would cause eventual motor failure. BTDT! A word to the wise.