That is incorrect. The specific chemical doesn't matter. Metallic paints have micro flecks in them and rely on both a glossy medium and those flecks having glossy reflections to maintain their faux-metallic look. When you apply matte, any matte, on top of metallics the reason they turn grey (or cease to sparkle) is because the matte screws up their ability to reflect. Imagine your metallic paint at a micro level being a big area covered in broken glass. It sparkles and glints. Now imagine putting a giant sheet of flat frosted glass over that, and it's not tough to figure out the physics of what is happening to the reflections and refractions.

TLDR - Never apply matte or satin on top of metallic paint. If you absolutely must seal it, use gloss. You need to have the light strike those micro facets and reflect off in many directions or you lose the metallic effect.

 

Woah, zombie reply here.

That said, any top coat with acetone, even gloss, will absolutely ruin a metallic finish esp in model/rattle can paints. There is a reason automotive top coats do not contain acetone, and there are many hobby level options that also do not, regardless of the sheen level you choose. Acetone and paint do not mix, and acetone and plastic make it an even worse combo.

I understand what you think you think you are saying, but your science is incorrect overall. I've personally used matte/flat finishes on metallics that did not contain acetone that do not do the same thing to the paint that an acetone based does. Something wax or resin based in a flat sheen will only dull the metallics, not destroy them.

 

Well yes acetone can potentially eat the paint depending on the type and also the concentration of acetone in a given sealer you are correct. But my main point was any matte will always ruin metallic effects. I teach classes on this, if you don't believe me I challenge you to paint metallic on the back of a plastic spoon or something metallic (flake or chrome, doesn't really matter), twice. Matte coat one, observe the uncoated vs the coated. It is due to matte being a micro frosted surface and having refraction and reflection qualities that does not allow for specular highlights. Specular highlights, or hot-spot sharp reflections and bounces, are the key quality that makes something appear 'shiny'. Killing those sharp hotspots is the entire purpose of matte, thus, the incompatibility.

PS - yeah sorry for the necro, I was searching for the most durable topcoat types I could use on a repainted toy. I am used to competition modeling and it does not need to withstand much wear and tear. Was wondering if there was some secret sauce toy customizers had beyond the usual testors/tamiya/liquitex/misc boutique modeling matte/satin/gloss. This thread came up in my search results and I thought I would share since I know many, many a pro-painter that has lamented ruining their work by applying matte to surfaces that need to be sharply reflective to mimic the intended material.

 

I'm not the robit police so no worries on the necro, this forum is supposed to be a learning place, so personally I welcome the discussion. On this one tho we are going to have to agree to disagree, you're welcome to paint as many spoons as you want, but I only use resin or wax based top coats anymore, and mostly only on real cars. I, like so many of us, have way more ideas for customs than I actually have the time to do - but one of these days I'mma come out of retirement and finish a few of them for sure!