ancientsociety on the WWPD forums said it best when he described a primer as "True primer is specifically formulated to increase the adhesion of subsequent layers by increasing hygroscopy and porosity. In the case of metals, primer also acts as a barrier against oxidation. Paint and primer are two very different mediums and its important to point this out to beginners." Full Thread Here
Maybe? Makes sense logically as water and air are need for oxidation and the varnish keeps those out.
- Orange = Acceptable...slightly less than the standard. Appears to be extra build up of primer in deeper recesses. This shows up as whiter areas than the rest of the figure. It might be an optical illusion, but again was only slightly less than the standard.
- Red = Less than standard. As expected, the uncut primer did clog enough detail to be noticeable.
- Blue = Acceptable...in between the Orange and Yellow samples.
- Green = Acceptable...Very minor clogging of detail similar to Orange sample.
- Yellow = Could see bare metal on 4th pass
- Orange = Could see bare metal on 3rd pass
- Red = Primer showed no changed
- Blue = Undercoat showed no change
- Green = Primer/undercoat showed minor wear after 5th pass (Could begin seeing bare metal, but there was still a THIN coat of primer over it)
- Red = No wear after 5th pass
- Blue = No wear after 5th pass
- Green = No wear after 5th pass
From Right to Left Yellow-Orange-Red-Blue-Green
Conclusion: As long as you use a gloss varnish with Matte varnish on top of that, a Black undercoat whether airbrushed or brushed/blown off generates the same "protection" as a Primed model that has been gloss and matte varnished. Add to this detail on 15mm models that is preserved with an undercoat that I am looking for and I have my winner. The one thing that you should not do is thin your primer with water. That was a clear negative no matter how you look at it.