I also think that it is only used as a mask and not for marking the blade. Also they are using a chemical bath to take it off.
I record "Extreme Makeover Home Edition" every day, and the "How it's made is broadcasted right before that, so I always have the last 5 Minutes of the show on my harddrive. Since we are 4 years behind in Germany, with Extreme Makeover, I wonder if it takes 4 more years to see this episode of "How it's made" live
Andrea