The carburetor bodies and airhorns are not plated first. They get a bath in chromic acid, just like the factory.
We have special procedures that we use, developed over the years, and too complex to describe in public forum.
Basically, it's time, temperature and how much concentration in the solution, combined with how the castings are prepared before they are dipped.
The preparation has a MAJOR impact on the final results, as a uniform surface finish must be established, and all oil, grease, etc must be removed from the castings.....Cliff