First let me say that you should only apply a very (VERY!) thin layer of primer to your models. I'll look at why below but when I say "thin" I mean that if you're priming white over a grey model you should still be able to see grey through the primer.
If you apply the primer too thickly you'll loose detail on the model and create a smooth layer that will be LESS effective at helping paint to adhere to the model (see 1, below).
Now let's look at why you prime a model:
- It adds "teeth" to help paint adhere to the mode
- It helps in finding mold lines and surface defects
- It allows you to use thinner layers of paint
1. By using a thin layer of primer you create a very slightly rough texture on the model. This isn't the rough texture, often called "orange peel," that you get with a bad primer application but a very thin coating of paint. This thin coating creates tiny, microscopic peaks and valleys that will give the next layer of paint somewhere to rest. This keeps it from flowing more freely across the model and helps stop it from being rubbed off as easily with handling as there is more surface holding the paint in place.
2. Many are the mold lines you'll find when you add a thin layer of primer. This gives you a chance to clean them up, and re-prime just that section, before moving on.
3. By adding "teeth" to the model you can use thinner layers of paint, and thus loose less detail while painting, because it's easier for the second and subsequent layers to adhere to the model.
4. Pre-shading is something I'll cover in a future tutorial as it really is a topic of its own. But if you have a question about it please let me know in the comments or via email.
There are other reasons to prime a model but I won't cover those here. If you have a question I'll be happy to answer it in the comments, via email or with another tutorial though.
In the interim here's a look at how I primed one of the Beveled Edge "Trench Works" 60mm 02 bases.
And that's really it. Tight controlled burst of primer to create a thin layer of "teeth" for the next layers of paint to adhere to.
It's worth noting that the 60mm base in the video is going to be used with one of my models and will eventually be shades of black and brown.
Remember, if you have a weathering or detailing question you'd like answered just drop an email to misterjustin at secret weapon miniatures dot com.