For the past few days I've been testing the paint on a piece of scrap Sintra with a bit of Worbla stuck to it, to simulate what an actual piece of the armor would be like.
First, I tested a spray-can type of primer, to see how well it would coat the two different surfaces. That part went pretty well. It took three coats to really cover the Worbla, but that was mostly because the Worbla has a rough-textured surface. I could actually sand the Worbla first, and then prime it. But I wanted to see how well the primer would smooth out that roughness. So yeah, three coats did the trick. And since the primer is black, and the Sintra is black -- and also the Sintra is pretty smooth -- I only need to prime the Worbla areas and I can pretty much ignore (not prime) the Sintra.
The second step was to actually try some paint. This was, in a word... disappointing. I bought a metallic silver paint that someone else had recommended, but it is really thin and doesn't cover very well. After two coats, it still has not completely covered the black Sintra or the primed Worbla. I think a third coat would do it, but I am surprised, and disappointed, that it's taking that much. And after all that, it does not really look very metallic to me anyway.
So, now I am starting to reconsider how I want to paint this armor. And what I am thinking about is actually painting the silver on first, but then painting a coat of some color, maybe something blue, so that it looks like colored metal. This would (hopefully) cover up the fact that the metallic silver doesn't really look like metal, while also (hopefully) add a bit of color to the costume.
Why do I want color? Well, for one thing I have realized that my mail shirt is actually black, rather than plain shiny steel, meaning that having the "metallic" pieces layered over the mail might actually look kind of silly. But if I painted the armor pieces in a darker color, they might blend better with the black chain mail, and give the whole costume a better look.
So yeah, I've got some minor frustrations here but am trying to figure out a good solution to fix the way things are looking now. After I do some more testing with the color, I will post my results. Hopefully later this week. I only have about ten days to get this thing done, so I really need to move fast.