Everyone has their own tools, supplies, and techniques for weathering. I thought I'd share what I keep in my weathering kit.
You can never have enough vessels to mix paints, washes, and pigments in. I use bottle caps for mixing paints and washes but I prefer to use sealable containers for mixing pigments.
To create a patina effect on copper and bronze I have a technical paint from Games Workshop, a three part kit from the craft store, and even a powder from Secret Weapon Miniatures. When applying the powder I mix it in mineral spirits before applying to the model.
I really like the three part patina kit I got from the craft store. When used together, they provide a much greater variation in color than the GW or SWM patinas do alone.
There are a lot of methods to getting a good chipping effect on a model and I use them all. There are two basic methods of chipping, additive and subtractive. Additive is when you use a brush or sponge to paint on the appearance of chipping paint. Subtractive is when you apply something under a top coat which allows you to remove paint. AK makes a series of chipping fluids which go on under your top coat and allow you to rub or pick away at the top coat. You can also sponge on a masking fluid and rub off later, or apply some salt to your model prior to laying down your top coat and flake off the salt.
The major advantage to the subtractive method is that you can pre paint a great weathered effect under your top coat and reveal it in a very natural way. This is harder to do with the additive method but you do have far more control, however, sometimes having too much control can lead to a very forced weathered effect.
Oil washes are achieved using oil paints thinned with mineral spirits. I keep brown, black, and burnt sienna on hand. A good supply of cotton swabs helps when cleaning up excess wash.
There you have it. That's my complete weathering kit. I'll be doing some additional weathering tutorials in the future using these items.