Iv made homemade fitlers out of alsorts, Green use a cider bottle/ lilt bottle, Yellow/orange get another cider sort of bottle, Red use a tizers bottle ect ect, (Just look out for a colour you fancey)
Then i just cut it lenght ways up the bottle cut top and bottom off, Get a ceral box cut it open down one of the corners so it opens right out like a flat pack, Unscrew your head on your lamp and wrap the cardboard round it so it fits JUST as it will have to slide on and off easythen trim all the extra cardborad off, Then just do lashing of tape round the cardboard so it goes ridged, Then