"Washes are used to accentuate panel lines and detail and to add a bit of interest to the surface of the model." - Mal Mayfield [ HOLDFAST ].
Washes can also be used to create and unify diverse weathering effects and finishes. I have been dissatisfied by traditional methods of making POL (Petrol, Oil & Lubricants) stains, of simulating dust and dirt accumulations, and especially large areas of rust. Rust is often more than just orangish streaks running down vertical surfaces. It can be on a flat horizontal surface where water has collected and seeped under the paint, attacking from below. POL spills can collect, repel and wash away particulates. Dust and dirt on a moving, jostling, vibrating machine, can be agitated up against raised items and into corners. All three of these phenomena in unison can produce complex patterns that ordinary weathering techniques just can't capture, at least not without hours of delicate, dedicated effort.
Seeking more authentic methods of mimicking these effects, I hearkened back to my art school days. With various media, I experimented with ways to create different effects on models. Three media in particular have been very successful; guache, india ink, and the new water mixable oil colour. Distinct effects can be created when mixed with equally unconventional mediums, these being ammonia, vinegar and Future (Johnson's Klear), as well as good old windshield washer fluid.
These washes can produce feathered, graduated effects which I once could only create with an airbrush. Unlike spraying these, this is a quick and easy way to cover areas large and small. And if you are that rare modeler who makes a mistake, you have time to dilute, increase, wash or wick the error.
With the following washes I used the same amount of media and the same amount of medium. You can see that ammonia, Future, vinegar and windshield washer fluid produce the same basic effect regardless of the media. If you are concerned about interaction with the paint, note the white Matilda is auto spray enamel, the ME-262 is Polly Scale acrylic and silver auto enamel, and the bulkheads are Model Master, Tamiya, Testors acrylics and enamels. I have noticed no detrimental effects of the mixtures and the paints. I usually apply the wash over a surface brushed/sprayed with water.
An old weathering standby, India Ink is light fast and permanent, and also totally waterproof when dry. It dilutes with water and, used by artists for a variety of purposes, especially calligraphy, is very "wet" - flowing easily. India Ink is also available in many different colors.
India Ink + ammonia:
when applied the wash covers everything. As it dries, the ink surrounding raised objects is pulled toward the center of the puddle creating a rough edged outline effect. Upon flat areas it settles uniformly.
India Ink + vinegar:
vinegar pulls the pigments inwards but not as densely as ammonia. It leaves slightly lighter saturation of pigments around the periphery of the puddle. The wash dries uniformly and pulls the pigments inwards toward raised items, leaving a nice gradation of light-to-intense saturation.
India Ink + Future:
as with vinegar, Future pulls the pigments inward, but settles a uniform saturation of pigments with minimum puddling. The wash pulls the pigments inwards toward raised items, leaving a nice gradation of weak to intense saturation.
Water Mixable Oil Colour, "Water-oil"
This is oil paint, yet thins and cleans with water. It gives many diverse effects and comes in many colors. As a wash, mix the water-oil thoroughly or you will find small gobs of the paint in the wash. This can be good if you so desire independent gobs that can mimic rusted chips or mud spatters. Beware that the buttery paint can lurk in your brush and deposit the paint on an edge where you may not see it until after the carrier dries. Usually your fingerprint is the first hint that it was there.
Water-oil + ammonia:
the wash quickly begins drawing the paint inward to puddles, and 'roughening." When dry, it gives a rough edge effect, such as water that has attacked metal and left irregular areas of rust.
Water-oil + vinegar:
the pigments lie in the wash more smoothly, and dry in a gentle gradation.
Water-oil + Future:
keeps the most intense concentration of the pigments. The heavier Future pulls the wash off of raised areas.
Guache is finely ground pigment watercolor that is opaque and dries matt. It usually comes in small tubes.
Guache + ammonia:
ammonia deposits guache with an edge.
Guache + vinegar:
dries dark along edges, with a grainy texture.
Guache + Future:
again the Future accentuates the intensity of the guache leaving an even coverage.
Windshield Wiper Fluid
This is the ubiquitous liquid we pour into our automobile washer reservoir. Media flows freely with it as a medium. Note that guache dries with a "crackle" effect.
Model Paint Washes
This is how common artist's products behave as washes with ammonia, vinegar, Future, or windshield cleaner. How do these mediums behave mixed with model paint? I chose Tamiya and Polly Scale to demonstrate. Both paintsí washes behave much like the water-oil, guache, etc. However, vinegar does not dissolve the paint, rather isolating it and depositing it in globs, leaving unique patterns when dry.
Finally, how do these methods compare to traditional washes? Those of you who use washes can compare them with your own effects and experiences. For those who have not use washes, I present as the final example the common wash of oil paint and mineral spirits (white spirit). For contrast I applied it right over the dry Tamiya/Polly Scale washes. My example dried rough and choppy, pulling the pigments away from the center of the puddles. This mimics many of my vinegar washes.
Conclusion, Caution, Disclaimer
In conclusion, allow me to offer some caution and disclaimer. Vinegar is a weak acid and ammonia can irritate your eyes and nose. My disclaimer is that I am not a chemist, nor even well-versed in the interactions / reactions of any of these chemicals and products. Use at your own risk. I can only report that I do not feel that I've suffered from them. Also, I have noticed no ill effect to my enamel, lacquer and acrylic paints by my washes. Depending upon the finish I seek, I often apply all of these types to my models, as needed, both before and after the pre-decal gloss coat, and before and after the flat coat. I gloss with either Future or Polly Scale Gloss, with Dullcote, Polly Scale Flat, or Floquil as my flat finish.
Another caution is that ammonia dissolves Future almost immediately (see my example Ammonia VS Future
) Thus I have not applied my ammonia-based wash over a gloss coat. Alcohol will fog Future just as it will Dullcote. Some windshield cleaning fluids contain ammonia and/or alcohol. Plan your weathering with that in mind, lest you ruin your masterpiece. Of course, one of the beauties of Future is that if you mess it up, strip it with ammonia and re-apply - simple!
Enjoy your hobby. I hope that these ideas will be as helpful and enjoyable to you as they are for me.