That warm up method you found is actually pretty smart for thick color glass. Cobalt blue can be a real pain with its different cooling rates. Palmer.val has a point about quick breaks with water, but on a tube that big, I've had the score run on me every time with the cold snap method. What finally worked for me was a diamond band saw, but that's a whole other tool. For hand breaking, your light score and even heat seems like the right call to avoid those chips.