Dipping vs blasting

The cars weren't completely submerged, so those parts would be bare. The assembly line dipped down into the vat and back out as the car moved forward. So the primer line is higher on the front and back of the car and lower in the middle. Really thorough restorations attempt to replicate this effect.

The body was spot welded together before it was dipped, so nothing to "burn through" I guess the paint probably wouldn't get into the lap joints and pinch welds so well. But at least the hollow cavities would be painted.