Another finish under the hood and a couple other places that is usually incorrect is the Manganese Phosphate. The hood hinges, caps on the shock towers, hood latch, parking brake and gas pedal bracket have Manganese Phosphate. If the parts are painted it causes them to stick and not function properly. I just ordered a gallon to do some parts for my Q code build.
You mix 14 ounces of the chemical with a gallon water that is heated to 190 - 200 deg. F. It only takes 8 - 10 min. to do the finish.
Before you put parts in the solution you have to clean all the rust, grease, oil off and glass bead the parts. Oven cleaner is good to get all the grease off.
Right out of the chemical you spray with WD-40 and do several times.
When I do the hood springs I cut a piece of 1/2" conduit long enough to stretch the springs to leave a gap between the coils to allow the chemical to work.
We have a local place that I buy the chemicals from Palmetto Enterprises 1. For the gallon I got it was $130.00 + shipping. You can get by with a quart of the chemical by adding glass jars filled with water to raise the levels in your tank. You have to use Stainless steel or porcelain coated containers. I found a big stainless baking tray large enough to do the hinges and parking brake. I will do a how to when I do them which will probably be soon. I twisted my back changing door on the Q vert so barely moving today.
There are various fasteners, nuts, bolts that also use the Manganese Phosphate coating but I do not have a list. It is commonly called Parkerizing used on guns.
The Slop Gray painted parts is another area done incorrectly on most cars. All of the cars at the Mecum auction are done wrong for the Manganese Phosphate and most of the Slop Gray.