Knocking out the base coats!
I've come up with an interesting way to do base coats. Being a fairly impatient painter. (this I'm sure has been around a while I just thought of it recently though, so It's new as far as I'm concerned) I did this technique to my necrons and a commissioned soul grinder a while back. Gradient base coats are a great way to add depth to your army or model and after you finish you won't be able to tell that you even did anything at all. It's one of those subtle things that you won't see but your brain will register as the model looking better and you just assume the brush work must be better than normal. However its just a rattle can wonderland of a trick. :P I'll use my current project as an example.
For my Khorne army I assembled all the models and glued on my sand, rock, quark mix to the bases. I do this before I prime or paint because the primer and paint acts as an additional adhesive and protective coat to the sand keeping it down better. I first primed all the models all over using Rust-oleum Rusty Metal Primer. This both primes the model and gives us a good base of dark red/brown to work up from.
This is where you start getting artsy with the rattle can. I now took Tamiyas Color Dull Red and stood all the models up and leveled the can at about a 45 degree angle staying about 10 inches away and sprayed lightly all around each model as to not cover all of the Rusty Metal Primer.
Lastly I took Tamiyas Color Bright Red (this is a gloss) Leaving the models in the same position as above I got directly over the models at a 90 degree angle staying at about 14 inches away and gave a SHORT burst to each model.
Now the downside to this technuique on these particualar models is that I go from a Flat re/brown to a satin dark red to a gloss red. This can be troublesome while you paint as the differing degrees of reflectivity may think that as your painting it looks off which after its finished and all dull coated clear will bring this in to cohesion and make it perfectly fine. However if this bothers you there is two ways to fix it. The First being only use all flat paints. (I used the gloss bright red because I couldn't find a flat bright red and I personally pretty much exclusivly use Tamiyas or Mr. Surfacers products.) The second way to fix this is simply spray your models with a light coat of flat clear before you start your brush painting.
The upside to this is it creates natural highlights and shadows on the models. For instance my models have a gradient (blended transition) from dark red/brown to medium dark red to bright red. It's basically cheating and taking advantage of our canvas being 3D.
This in no way means I'm done. I still have some washes and highlights to do. About 6 steps in total to finish the skin on my red demons. You may think that after my 6 steps or so of brush paint then what was the point. Well like I said earlier It's a subtle effect that your brain wont register or see. You won't say "oh he used a bunch of rattle can paints for his base coats." You will think the model is painted better than a model using the same brush steps but just being based with a solid color as the foundation.
Side Note: I use Tamiyas and Mr. Surfacer's Primer paints and clears because the atomize very small. When using this technique I wouldn't recommend paints like Testors as the spray isn't as fine and holding the can away at 14 inches and doing short bursts your more likely to end up with spots or speckles instead of a smoother gradient.