A catalytic converter’s ceramic brick looks solid, but it’s a honeycomb of hundreds of parallel channels, often 400 to 900 cells per square inch. Bare, that cordierite offers almost no surface for chemistry to happen on. The catalysis lives in the washcoat: a porous skin of high-surface-area oxides, typically gamma-alumina at 150 to 200 m2 per gram, blended with ceria-zirconia for oxygen storage and carrying the platinum, palladium and rhodium that do the actual work. The hard part isn’t the chemistry. It’s getting a controlled, even film onto the walls of channels a fraction of a millimetre wide, hundreds at a time, without plugging any of them. This is where vacuum washcoating earns its place. The brick is dipped one end into a metered charge of slurry. A vacuum applied to the opposite face draws the slurry up through every channel in seconds, then a second, stronger vacuum pulse purges the excess back out. What stays behind is a thin, adherent layer whose weight can be dialled in ...