I'm doing a lightweight part, the helicopter canopy mentioned in my other post, and it will need some accents of color. Maybe about 20% of the surface, probably red, and the rest left clear carbon. I'm trying to decide the best way to do this. One thing i considered is no paint and just use vinyl stickers after the part is complete. I have a cnc that can be used with drag knife for cutting any vinyl shapes I might want. Other option is painting but i don't know what the best method would be. In the mold before lay up? After the part is done and paint the outside? Also it will most likely be somewhat detailed patterns so I'm not sure how that would be done inside the mold on top of pva before lay up. I'm sure you can't use masking tape and expect it to peel off without taking the pva. I also saw the post mentioning using vinyl stickers in the infusion which also might be a good option if that works well. 
What will give the lightest weight and/or best look? Maybe one is a sacrifice of the other. Vinyl stickers on the outside would be super easy, but not sure how that will be for weight compared to paint, also probably wouldn't look as nice as something applied in the mold during lay up. 
Suggestions?

I would expect a thin layer of paint to be the lightest method. You would need a super thin vinyl to compete with a thinly sprayed paint layer.  You could mask the part in vinyl using the cutter to cut the shapes for you. Then peel it off once painted.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Don't use pva, but a good modern release agent, and your problem is solved.

Thing is, even if you do it in the mould, ideally you still need to rough up the surface of the paint to ensure a good bond with the epoxy - some paints will bond without any prep, but not all do. Some will just peel straight off after you demould. It isn't something I would commit to without testing first.

Post painting is definitely the easiest way. Either mask up before scuffing the surface, or use a clear adhesion promoter. I've never tried an adhesion promoter personally, but the spray painters I know will use them. They prefer a mechanical key, but they say the adhesion promoters do a decent job when necessary. 

After looking up specs and doing some calculations, it looks like vinyl decals for color is gonna be the way to go. Very easily make any complex patterns I want and weight is pretty minimal. 150g/m and my canopy has a surface area of 0.15m so if I cover a third of that, it's about 7g of vinyl on a 110g or so canopy. I can live with that. Also nice for the ability to remove it and do something different.