Marketing. People want to see what's inside and food in jars looks more home-canned than food in cans.Then why do alot of vegetables come in clear containers? They should just go ahead and start packaging them into opaque bottles.
Magus I use the glycerin from the bio fuel I make for bar soap Made 1600 gallons of fuel for the farm last year. I use the lye and methonal method. PhilTurn it into bio diesel if you have a lot of it,dose your slop barell in your methane kit if you don't.
To the best of my experience,soap requires animal fat using the lye method.