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So, about 6 to 8 months ago I decided to attach my metal Incubi models to resin bases. Unfortunately I soon lost my motivation. With the arrival of 6th I've become re-energized. The thing is when I came back to my paining desk I noticed that the shiny metal miniatures now had a black coating to most the model. What is this?

I live in an area with very high humidity and my painting desk has a window near by that allows the sun to crawl across the models. I assume this is some kind of rusting effect, but is it? What I'm worried about is that this will somehow effect the models when I go to prime and paint them. Should I just ignore this blackening and prime over it or is there some easy way of removing this black stuff safely keeping in mind the resin bases. Any help will be greatly appreciated.

edit: grammar

I don't know what it is but it shouldn't affect the painting.

I have a bunch of old Tallarn models, the ones in blisters are still nice and shiny, but my others are a dingy grey-ish, but they look the same once painted.
Haven't found a way to remove it, doubt it can be. I've scrubbed them in Lysol and Simple Green...I'm sure it's some sort of tarnish/oxidation.

Probably just oxidation accelerated by the heat/UV exposure from their window position.

It isn't "lead rot" (no lead in GW since way before the DE metals were released), and most other oxide coatings aren't necessarily a symptom of "weakness" (aluminium and Tin both readily oxidise to protect the surface from further damage (as both Aluminium and Tin Oxides are harder than their metals).

Almost certainly oxidation on the models. I can't imagine that it would effect the painting very much once you have primed over it.

Never heard of metal minis blackening - normally they develop a light grey/white film, like TheCupcakeCowboy describes. I'd give them a good wash, scrubbing with a stiff brush. This will clean them for priming, first and foremost, and knock off the blackness if it's merely a settled residue. If it's metal that's reacted, instead, anything that stays is probably safe to allow to do so. If you really want them bright and shiny again, take some fine steel wool to them. That's what I do to smooth surfaces and remove dusty oxidation when prepping metal.

Seen everything from black, to shades of red and brown all the way over to evil white powder on metal. The specific metals in the alloy as well as the heat with which they are cast (and speed at which they cool) will impact the color of the oxide which forms.

Unlike lead rot or iron oxide - it normally will not be dusty at all, but rather a very hard surface coat. Very similar in a lot of ways to anodized aluminum as chromedog mentioned.

Give them a good scrubbing with a tooth brush and a grease cutting soap (Simple green or dish washing detergent) to make sure it isn't something like oil/acid from fingers touching them and then paint away.

A cheapo brass brush from Harbor Freight will do great job of removing that oxidation.

tim

Thanks for the replies. I was pretty sure that it was some kind of oxidation but I'd never really read anything about it happening before. I've since learned that I can scrape or sand the oxidation off but being that it covers most of the models it is fairly counterproductive as it won't show after priming. Once I'm done with some other preparations (scraping off some mold lines, green-stuffing some holes in the bases) I will probably go ahead with washing and priming.

@oadie: The idea of steel wool seems like a good one but I am unsure if I would be able to most of the fiddly details of the models.

@timd: Have you ever done this before? I'm just a bit leery about taking a brass brush to my metal mini's.