I wanted to take a minute to write about priming. It's something a lot of modelers do before painting a kit. Though generally a good idea, it's not always needed.
When to use primer...
- You have a rough or uneven surface - Primer does a good job of evening out surfaces. If you have a kit that has heavy sanding marks paint may not do a good enough job leveling them out. If you find yourself in this scenario an easy fix is to prime (typically you should work the pieces with a lighter grain of sandpaper first). If the surface has pot marks or other defects priming can help identify them prior to paint and provide a good working surface for sanding and filling. If this is your main concern consider using something from Mr. Surfacer.
- You're going to a lighter colour than the surface plastic - This is the most common reason for priming. Any time you want to go to a lighter colour should prime before hand, providing a lighter and more consistent surface for any paint going on top. This is especially important for vibrant and bright colours. The look of many paints will be dependent on the tone below and bright colours will pop considerably more if the underlying colour is also bright. Darker colours won't be impacted nearly as much and subsequent coats will help close the gap.
Here are some examples of how basic colours look depending on the base coat below them. If I'm painting a like colour to the plastic underneath I generally don't prime as the effect is generally negligible.
- You're going to paint on a multi-toned/coloured surface - As paints will often appear differently depending the surface colour they're applied on top of, having a base surface with different colours can result in tone differences amongst pieces. Sometimes this is results in a desired effect (i.e. pre-shading) but when unintended it can make a kit look awkward.
- Your paint has difficulty adhering to the plastic - Sometimes paints will have difficulty adhering to plastic. A good coat of primer creates a nice consistent coat for paint to stick to. Most modern kits don't have this issue and many older ones just need a wash before painting. Resin, on the other hand, needs both a wash and prime for best results.
Note that covering with white primer is going to be time consuming and require a lot of a lot of coats. Whether it's the lightness of the white, or a thinner mix that's used, you're going to spend more time applying coats than simply going with a darker colour. Because of this it's important to make sure all your pieces are coated to the same extent. If not you may assemble and find that two concurrent pieces, having not received the same coats, feature different tones. It's also worth noting that, in my experience, shades of red are generally the hardest colour to completely white out.
Any hobby primer should treat you well, whether it's from Mr. Color or Tamiya. I recommend visiting your local craft store and picking up widely available Krylon spray primers. They comes in black, grey, and white and are cheaper per volume than most modeling specific brands. The key part is that it generally sprays very well and drives thin and smooth. Though, like any paint, too much in one area during a coat and it will drip or pool. These should be used outside as they tend to put a lot of particulate into the air (white especially). I've used them extensively over the years with consistently great results.
I haven't primed with my airbrush yet and, depending on who you ask, results from various brands & methods come off as too inconsistent for me to comment on.
Gelgoog Guy asked me to me to mention The Army Painter primers. The Army Painter line offers a whole bunch of coloured primers that look fantastic. Check back in the future as I plan on testing them out for The Guide.