This quick 15 min experiment  that was conducted on a 1/35 scale Italieri, Opel Blitz truck door.

The piece had previously been painted with a base color of Floquil, which was then given a filter of Windsor Newton "Cobalt Blue" artists oil paint. As soon as the filter appeared to be dry,  a round tipped brush was used to randomly dab Gum Arabic along the edges and approximate areas where chips were desired. The Gum Arabic does not hold well (likely due to oil paint the filter) and will shortly begin to lift from the surface. Over this was promptly sprayed a coat of  Tamiya acrylic paint from a spray can. When the Acrylic paint surface was dry to the touch, Tamiya masking tape was used to lift of the Painted areas of Gum Arabic. Because the paint hadn't been allowed to completely cure/dry, the tape lifted of areas of non Gum Arabic also.....this was also partially caused by me pressing  the entire surface of the tape down onto the paint. This  issue though can easily be controlled by using smaller pieces/edges of the tape.

This was followed by a light wash of Raw umber artists oils. An 0/18 brush was then used to paint some Vallejo "SS Camo Black Brown" and "German Camo Dark Grey" into some of the chips to indicate deeper scratches and areas of bare oxidized metal. (The scratches were made using a pin, and then lightly lifting the edges with the masking tape) Onto these darker chips were added some diluted pin washes of Windsor Newton "Burnt Umber" artists oil paint using a 0/18 brush. 

The entire surface was then given a light dusting of MIG "Europe Dust"

I think this technique has a lot of potential. It's easy to work with and the effects can likely be adjusted with how/where the Gum Arabic is applied, how thick the Acrylic is applied, and how long the acrylic is allowed to dry/cure, how the tape is used, and taking a bit more time to do the whole process.

If the  technique was combined with mapping on the base an top colors, and some other wear techniques ( brush painted chips, sponge dabbed wear, etc), some very nice/interesting results could be obtained. 

I also noticed that if areas/spots of the GA were left under the acrylic, it had the appearance of "blistered" paint. These areas could be slightly "picked open" with the tip of an X-acto or pin, to give a ragged blistered paint look...especially if some diluted rust colored pigment, or Burnt Umber oil paint were carefully flowed into/onto the area.

A notes on the experiment:

 The filter was applied before the Gum Arabic, not so much for tinting the base color, but hoping, it would cause/allow the GA to come off easier (as GA is water soluble and shouldn't bind with the oil). This technique has not been tried over acrylic paint yet, the base paint that was used here  is a petroleum based lacquer. It was used as both the primer and base coat in one, as it aggressively holds to the plastic. How the GA would react if applied directly over an Acrylic base color, or an Acrylic base color with a sealer coat such as Model-Master "Lusterless Flat" or Gunze/Mr. Surfacer "Flat Topcoat" would need to be experimented with.

by Marc Reusser

This  experiment  that was conducted on a 1/35 scale Italieri, 'Opel Blitz' ,truck cab side

Warning:  the images are not any great examples of model-building... merely intended to see how the chipping technique would work. The experiment is intending to represent paint that has chipped through to a previous layer of paint, and in a few areas to the metal below.

  This experiment was done using a mixed Floquil grey color as the base coat, then an artist’s oil-paint filter, followed by a brushed on coat of hairspray. The acrylic was airbrushed once the hairspray had dried for about an hour.

Chipping was done by first thoroughly wetting the surface then using a pin and/or pointed wooden toothpick to chip/lift the paint. The chipped areas were then followed by a wet scrubbing with a stiff brush to refine, shape, soften and/or expand the chips/areas.

Though a lot more work, and care needing to be taken not to dig into the plastic with the pin, I feel that the technique offers more control, than just "scrubbing" at the color.

This is  a test that was done in the same manner on another/different piece. The left side was chipped using just water and a stiff brush to "scrub" the acrylic paint off; the right side was done using the above described method. For me, the main difference other than control, was the pin chipped side did not leave the "color residue" in the chipped areas, like the scrubbing method tended to.

On the left are examples of the "stiff" brushes, with their cut down bristles. The right image is the hairspray.

Just for the heck of it I tried a  quick experimented with a "damp brush" application of Windsor Newton "Zinc White" Guache to add some color fading and weather/rain streaking. an This photo shows the same door as above after the Guache application.

It did give a nice completely matt faded finish....but one thing I found was that one needs to be careful, as the Guache will fade/lighten all areas, including the chips...where it looks like a light layer of dust. Also one can see where it appears that the Guache has settled above the horizontal ridge on the door....though it is more intense on the photos than in real life....this either needs to be removed or toned down with some pigment weathering or an oil paint "pin/spot" wash.

These are far from "prime work", and definitely need refinement but for what they are worth, I thought they might be of interest.

This was the winter whitewash. I used an old scrap part from a Pz-I that had long ago been painted Dunkelgelb with Tamiya acrylics. I was trying to think of a workaround for the hairspray technique, and mapping with oils.

Using Vallejo #837 Sand Light, I brushed on highly diluted washes, about 6 or so, drying them in between with a blow-dryer. Over this I used about 4 washes of #853 White Glaze....again drying with a blow dryer in between. I wasn't concerned with even coverage...I just tried to avoid having areas of "puddling". I then used a small dampened stiff brush, and began "chipping"/removing the washes. I added some quick dark chips with SS. Camo Brown, , washed on some rust areas, and then added some MIG "Dried Mud" pigment with a brush.

Looking at it, I thought that this technique might prove useful in achieving a worn paint finish such as this on heavy steel.

Some quickie barrels. (4) 1/48-scale and (1) 1/35-scale. Painted with Vallejo and Life-Color Acrylics. Rust done using Windsor Newto artists oils, and Mig pigments For final use in a scene these would still need some dust, and maybe an oil stain near the caps.