sorry way too wet and messy to touch the camera at that stage i'm afraid.
-clean slate
-place riccia on it right to the edges, not too thick, just so you can see bits of slate underneath
-buy a transparrent hairnet (from a chemist, super markets only sell thick brown ones round here)
-place hairnet on top of riccia
-pull tight and tie off on underside of slate
-dump in tank and leave alone for 2 weeks to grow through and conceal the net
-hey presto riccia on slate.....
a 5 year old could do it. it's not hard at all just a bit messy.
do bear in mind it grows really fast. every week you can scoop off enough riccia from the surface to make another, it goes on and on. I could have carpeted the entire base of my 40G by now with the ammount of floating stuff that breaks off.
be prepared for some maintenance, if you ignore it you end up with a thick blanket on the surface cutting off the light to the tank and other plants..
hope that answers your question.
if you want a bag PM me your address, wont be long till i'm next on a clean up mission.