To keep this back on a technical level....
If you roll through this whole thread you will see the main bits changing in color somewhat.
I’m using most of the same chemicals, just in different strengths and combinations.
There is no “correct” way that I’m aware of yet, but the acid etch to open the pores is different for each chromate. I have officially tried out a handful more since I’ve started and the results are wildly different.
PH monitoring has become an hourly process while working with both the acids and chromates.
Surface prep and cleanliness is much more specific now. I’m using a cleaner that is designed specifically for zinc die cast. E163, Epik, and EPrep have been added to the roster.
I wish I knew what if any presoak Holley originally used. I’m inclined to believe that they wouldn’t need to since the castings were fresh and already clean on a molecular level.
The only reason I think they did use a presoak/etch is you can often see it’s tell tale trace of washing out the chromate in a few spots.
On another note, I’m only a handful of carbs away from documenting the calibration of every Ford Fe performance carb of the 1960’s. I hope to make this information available in printed form in a year or two. That isn’t for any glamour on my end, I’d just hate to see the information lost to time.