I've been asked this more than a couple times and figure its a relevant question so I'll post it here. When airbrush painting lead jigs or metal lure bodies do you undercoat or spray over bare lead?
I pretty much will spray bare lead without an undercoat or doing any prep work unless the bare heads have been setting around for a long time, then they'll get a bath in acetone and dried well before I spray the color. Some blades and other metal inserts come with a shellac coating and that can pose an issue if one decides to degrease using acetone. On most polished metal parts I use warm soapy water and a soft brush to de-grease and give them a good rinse under very hot running water. As for undercoating blades and such I am more likely to just cast those using both the polished brass [gold] and silver bodies so I can match the body color to the paints I plan to use. I may undercoat a blade bait or spoon with white if the finish is going to be containing white but for the most part I just spray over the bare metal.
I tend to favor transparent paint colors on most of what I spray including plastic lure bodies. If a plastic body is cream colored I give it a white undercoat. White bodies and clear I generally do nothing with to prep them for the color as I like the depth achieved by using transparent colors over clear bodies and over bare metal including lead. I use a lot of pearlized colors and those are most often mixed with some transparent color. I also use fluorescent colors, but those too are seldom used as is out of the bottle but rather are mixed with a pearlized or transparent color or both. There is a random ration in my head that I use when mixing these different colors together to achieve the effects that I want. Its amazing how mixing these three markedly different types of paint can yield such great finish colors on bare metal.
As many know I like working with the color-shifting pearl products used in after-market automotive paints. What started out in using these on the soft plastics I have also begun mixing these color-shifting pearls into black transparent or top-coat clear to apply over the hard plastic lure bodies and some metal bodied lure that have darker finish colors. These pigments are tricky to get accustomed to using but the results they offer are well worth the time in dealing with them.
So....undercoat or leave bare? A person has to experiment to figure out what he's looking for in the final finish. Transparent or opaque? There again a person likely needs to experiment to find exactly what he's desiring. For me personally I favor working on bare metal and I favor working with a color blend that leans toward transparent but hangs onto some bright and reflective qualities that come from mixing one or more colors and types of basic paints. I'll add that all of the colors I use are basic createx colors that are water based.