Metal paint works like the real thing because it's real metal -- it is the real thing. Bronze, copper, or iron particles are suspended in paint. When the paint dries the metal particles are exposed to the elements and oxidation begins. Some brands of metal paint make use of an activator that increases the rate of oxidation in case you can't wait for the natural oxidation process.
At DioWarriors we use the Modern Masters brand of metal paints and their rust activator. The process is simple: paint an object like you would normally paint, wait for it to dry, then apply the rust activator. The activator will begin working immediately, but the results might not be noticeable until a few minutes or an hour or more later.
The Modern Masters metal paint is water soluble, so it can be thinned. Never use the main jar as your primary paint source. Instead, put a little bit of it into a little cup or artist pallet. Keeping the main jar exposed to the air can cause some of the paint to dry and begin oxidizing.
Some points to keep in mind:
Clean up is easy and the paint is very thick so passing a cloth can remove much of the paint from a surface when it hasn't dried. Using regular brushes are not harmed through any chemical clean up -- just water. Like the paint, the rust activator is also water soluble -- simply rinsing the brush will clean it.
Working with metal paints are a lot of fun and they add a lot to realism. Using other weathering effects, such as paint chipping, can really add to the sense of realism. There's all sorts of various techniques you can use to further your weathering effect -- oil stains, soot, mud and grease build up -- that when used together with oxidizing metal paint can achieve a truly stunning look. But even without any other technique, the effect using metal paints can be just as stunning.
However, some caution: be aware that other paints that use metal particles will also react with the rust activator. Many metallic paints use inexpensive metals to achieve a metallic luster. Some brands use the actual metal -- real gold, real nickel or copper, etc. And some of those will react through ionisation when placed next to another metal. Even in paint where the amount of metal is small, there still can be an effect.
There's all sorts of reasons to want a heavily rusted machine. A rusted machine or object can really enhance the story of a diorama. Here are a few ideas:
Latest News blog thingy.