What I do is pretty easy actually.
- First wash parts with warm water and dish detergent as normal.
- I then wash everything down with Isopropyl Alcohol, for the grill - try using a damp Q-Tip (any cotton swab).
- I work with enamels, mostly Testors and some MM. I have a Testors
1/4oz. bottle of flat black that I added a "few" drops of paint
thinner/mineral spirits too so it's just a little more runny than
normal.
- Apply a "light coat" of the thinned flat black over the grill.
- Set the part to dry so the painted surface is facing up. That way
most of the paint will flow to the deep spots and leave most of the
chrome edges somewhat clean for the next step.
- When dry (within minutes) I clean up the raised edges that are
supposed to remain chrome. I usually use flat toothpicks, or those
craft sticks cut down (popsicle sticks), and just gently slide them
across the high spots.
I've tried semi-gloss and gloss, but those don't look too good to me on the grills.
I do the same thing for rims and any other chrome parts that need some
blackout work done to them. Some rims look pretty good if you use the
semi-gloss, especially if you want to match the car color.
Hope that helps get you started.