I’ve spent a lot of time researching methods of faking weathering, scale model forums have been good for that 😉
I’m curious about this stuff but at $120 a gallon not curious enough to buy it;
The sophisticated finishes stuff works pretty well and you can get from the craft store. I love that they have a full range of metals, brass, copper, steel… and a variety of patinas for bringing out different colors in the ‘paint’.
The basic idea is there is a paint which contains metal, and an ‘activating agent’ which is essentially a patina, to trigger the rust. Different metals have unique reactions, ferric metals tend towards orange while cupric metals towards green. Its a good idea to familiarize yourself with this process. http://en.wikipedia.org/wiki/Patina
I like to use atomized metal suspended with a bonding agent, then force it oxidize quickly.
I like to mix something like this:http://www.douglasandsturgess.com/mm5/merchant.mvc?Screen=PROD&Store_Code=DAS&Product_Code=FM-1044&Category_Code
As far as bonding agents, I’ve tried mixing it in paint, liquid acrylic medium, floor polish, all of these will work to some degree, but can tend to have a bit of a ‘plastic’ sheen to them. The other problem I’ve encountered is they can potentially seal the metal and prevent the patina from penetrating. One solution for this is to mix some of your patina with your paint mixture, but this can lead to a very even and unrealistic pattern. The thing to keep in mind is that you don’t want to seal the metal away from the chemicals and air, so keep the paint mix thin.
Most recently I’ve been using a mix of steel with plaster as my bonding agent. It can be a bit chalky, but the plaster holds water/oxidizers and prevents the seal as well as adding more texture.
The other possible bonding method is to spray an adhesive over the surface and apply the powder directly. Don’t go over board and grab the Super-77, you just need something subtle to hold the powder in place without messing up the rest of the surface, hair spray, or matte spray work well.
Now as far as ‘activators’, there are a few solutions. You can use water, a bit of salt will make it rust a bit faster, but that is not fast or dramatic enough for us, now is it? What we want is a stronger patina. These are essentially ‘oxidizers’ because they speed up the effects of air’s weathering on the surface of the metal.
The real stuff, used for treating bronze statues and the like, will work great;
But I’ve even had great results from simpler stuff, for example Hydrogen peroxide…