TSC: The Simulus Chamber: How I did it: Adeptus Mechanicus VTOL APC "Chauliodus"

- For forty years, your fathers before you and your older brothers played this game and played it well. But today the game is different. We have the advantage. -

Cpt. Ramius

Once completed the construction of the "Chauliodus", I had to fall into the same abyss and start thinking about how to adapt the subject to my love for oxidation. Since I'm not painting a land vehicle, I'd have to revise my standard technique a bit to maintain a reasonable level of plausibility.

As you should probably know, rust, corrosion and chipping have a certain charm on me. In other words, I am part of that "peculiar"category that on holiday stops to take pictures of things like cranes, containers and freight wagons.

"Grusavoy Vagon"

Unlike a tank, an aircraft is normally constructed using mainly aluminum-based alloys, so the oxidation process is completely different, as well as the type of stains and drips that occur on painted and unpainted surfaces.
Although it is a rather specific category, there is a ludicrous collection of photos of abandoned military aircraft thanks to the so-called AMARG, a.k.a. the most colossal "boneyard" of military aircraft in the world, at the base of Davis-Monthan in Arizona.

"Excuse me, I'm having a weathering eye-gasm"

Here you can get an idea, but the amount of material is simply astounding.
The dry climate of the desert allow us to appreciate how the paint tends to whiten, leaving here and there a glimpse of the whitish gray of the aluminum undeneath. Even the chipping pattern is less coarse than a similar steel surface. However, we can still have large areas with stains or even accumulated rust, thanks to the corrosion of rivets and armor plates.To obtain a similar result, we'll have to adapt a previously seen technique: the "windex fading".

John Tolcher is simply "The Man" for this peculiar chipping technique

As we had already said here, it's a weathering technique where the stratified paint on the model is "scraped" with an ammonia-based solvent.
It's a slower (and more tedious) procedure than the classic "salt and hairspray", but it's unsurpassed to achieve very clean gradients between the layers of color. Furthermore the correction process is extremely simple.

Our Good 'Ol One-Forty-Twenty

Differently from the other tutorials, I will abandon the usual "overall review" of the coloring process and focus on the errors and lessons learned while I'm trying to master the technique in question.

Let's start with a couple of fundamental considerations:

1)Contemporary history teaches us that common sense is everything but common, so it's better to avoid misunderstandings. Although they are rather common detergents, we must remember that we're talking about chemical agents that should not be underestimated. Gloves, glasses, a mask and a well-opened window are an endowment that every modeller should know rather well.

"Be a good soldier and use your protections."

2)The use of the homonymous detergent is not essential. A very simple solution of distilled water and ammonia (also perfumed) is cheaper, more controllable and easily replicable. I suggest you a good dose of patience and finding out your personal gold ratio in terms of dilution. Personally I tend to work with water/ammonia ratios between 4/1 and 8/1.

3)The key factors for this technique are the colors. Depending on our purpose we need something predictively sensitive (i.e. Tamiya, AK Real Color, Gunze Sangyo, Mr Color ...) or absolutely impervious (any enamel and most of the lacquers) to ammonia.
"Pure" vinyl and acrylics brand such as GW, Vallejo, Scale75, etc.) are not suitable.

4)The surface has a great influence on the final result. For homogeneous gradients we will need smooth, unobstructed surfaces. More pronounced textures or embossed details will be reflected on the result in a manner not dissimilar to a drybrush.

5)It works only with very homogeneous stratifications, so the airbrush is a must-have.

Now, to obtain the "boneyard" effect we need an aluminum-like metal base, which lends itself to being mistreated.
Even if healthy as a trip to Pripyat, lacquers like the Alclad series will allow us to achieve two birds with one stone: a metal basecoat and a surface impervious to ammonia. This should not be underestimated, since the brilliance of the metallic pigment will be dampened by any intermediate coat of protective enamel.

Shiny!

Once the base is set, we need two or more colors to be layered and then "transitioned" in a gradient with the solvent.
Be careful to not mistake the the number of layers with the achievable quality.
The number of colors depends only on the effect you're trying to replicate.
The quality depends, as usual, on how much you have mastered the technique.

Even in the stratification there is no absolute order between dark/clear or between saturated/desaturate layers. You can choose a light intermediate layer to enhance the fading, or a darker and saturated layer to accentuate the contrast. As usual, it is better to use a couple of scraps to test our combination.

A slightly darker gray will add more contrast

It is imperative to stratify homogeneously. If the layers are not regular, the action of ammonia will not be controllable either. So we will have to use the airbrush equivalent of the "two thin coats" dogma. Strongly diluted paint, and light sprays. A perfectly flat coverage is not necessary for all the layers, especially for the more superficial ones where the solvent action will be greater. The key factor is "being homogeneous".

You can see some salt here and there

Once painted, it's time to arm ourselves with the usual amount of patience, brushes of different hardness and tons of kleenex/qtips. Always using some reference material, we proceed by first gently dampening the surface with simple water and then with our mixture, weakening and/or removing the paint.
The hardness and the size of the brush (like the dilution of the solvent) affects the dissolution, acting progressively on the underlying layers.

You can see the boost in contrast given by the middle layer

On large surfaces it's easier to control the fades, on smaller surfaces you can resort to other "tricks" to scrape or dissolve in a more marked way the desired areas, such as the use of very fine "wet" abrasive papers (> 1500), toothpicks, or even a dull x-acto blade.

Most of the scratches are made with sandpaper

Being a technique that plays with stratification, nothing prevents us from combining it with the "salt & hairspray". Maybe weakening some areas with the hairspray and disturbing the homogeneity of the layers with a few pinches of salt.
Once the desired effect is achieved, the surface should be left to dry so that the ammonia evaporates, and then gently cleaned with the help of qtip/kleenex with just a little bit of little distilled water, in order to remove any dissolved paint residues. A transparent protective layer will seal everything, allowing you to handle the model again without any risk.

The aluminum is still shiny even under some dull coat

Being a process that we could define as "subtractive", one of its side effects is a desaturation of the colors and a general reduction of the contrast.
The effect is more accentuated, the greater the stratifications are. The stratifications also influence the shine of the metal base. By overlayering, the metallic pigment progressively turns towards an increasingly dull gray tone, invalidating a good amount of the effort.

Chicken Pox!

The desaturation can be corrected by working with an oil-based filter (or a glazing, if you prefer acrylics), perhaps giving a little more variety with a some stippling.

The warmer tones work better with a brighter middle layer

This returns vibrance (and variety) to the colors, but above all it restores the dulled contrast.
At this point you can continue as always with the normal weathering process, retouching where needed.
To further adjust the contrast we can add some edge highligh on scratch and rivets and emphasize the shadows with some targeted washing.
The process can also be applied in a similar way to the interiors. In my case, I've added some further aging with some dark rust sponging some "old-fashioned" brush scratches the hardest points.