Thinning, mixing, spraying and ‘washing’ with water-based model paints


Because Polly Scale, Testors Model Master Acryl and Vallejo paints are clearly water based, I’ve used distilled/deionized water, or tap water, to thin them. As in anything with water-based paints, you start by thoroughly stirring, then consider your goal. Remember the stirring mantra, stir until you are sure its done, then 1 more timed minute after that. I’ve water-thinned Tamiya and Gunze-Sanyo paints as well, but I’ve never been completely happy with the results I get thinning Gunze-Sanyo. Both companies offer a thinner and if I had to spray one or the other’s product, tomorrow, I’d probably experiment with those thinners.

If you’re going to thin a water or alcohol-based paint for spraying, you probably want to pour some of it into a mixing/storage jar. People will tell you to never return thinned paint to the container it came in, but I’ve done it and nothing particularly bad happened. Poly Scale seems about right for brushing right out of the bottle. Model Master Acryl glosses seem a bit thick, and their flat paint about right. Vallejo’s little 17ml squeeze bottles seem just right for brushing, out of the bottle.


For spraying or air-brushing, the paint should be thinned to the consistancy of whole milk. A little thicker and heavier than skim milk. This is a bit thin for hand brushing, which is why you should consider keep the thinned paint separate from your main supply.

Distilled or de-ionized water have the advantage of no mineral content to react to the paint. I’ll never forget the 1/72 Space Shuttle kit I decaled using tap water… which gave me rust stains on just about every marking! It shows up very well against white…. But I mostly use tap water and I can’t remember a problem in a long, long time. For spraying, if I want a thinner that will evaporate faster than water, isoproyl alcohol has always been my first choice. The 70% alcohol/30% water “rubbing alcohol” mix from the drugstore is fine. Use equal parts rubbing alcohol and water, for starters. Denatured ethyl alcohol might work as well. Experiment.

I’ve used my trusty Badger 250 Paint Sprayer for decades, with water and water/alcohol thinned water-based paints, especially Polly Scale, Works great. A number of people in my modeling club, The Silicon Valley Scale Modelers, airbrush with Gunze-Sanyo and I’ve done one airbrush paint job using it myself, with my Pasche double action cheapie ( model “H” or “V”). Thin, light, coats work great. Expect 3-5 to cover.


Mixing water based paint colors can be very rewarding. Start by stirring the paints you intend to mix. Use a plastic lid, white or translucent, as a mixing bowl/container and put a drop of each ingredient on it. Use a fine paint brush to bring a bit of each color together in the middle. When you think you have the proportions, roughtly, try mixing by drops, to see how it’ll go. Always put in less of the strong color, more of a mild color. Less black, blue, and red, More white, gray and pink,

Now paint it onto something, using a good brush: the outside of the jar lid, a parts tree, the inside of some part, a light-colored ‘utility’ model kept for the purpose. Just like oils, the water/alcohol based stuff changes color as it dries. That’s why I started painting well stirred paint onto the lid of its container over 30 years ago. Its a happy habit.

I’ve sucessfully used Tamiya gloss Red to mix with Polly Scale (railroad) Utility Orange, and made minor mixes of Gunze-Sanyo, Tamiya, Polly Scale and Model Master Acryl in various combinations, but they ARE different chemistry systems and don’t mix as readily across product lines as I would like. (the Red Tamiya tended to separate from the Orange Polly Scale, if too much water was used as a thinner. I’ve mixed Vallejo and Gunze Sanyo blues, and mixed that with Polly Scale white, and got more or less what I wanted. Nothing has turned a wierd color or started smoking, but I wouldn’t mix half of one brand with half of another- if the proportions are that large, I use the same brand for both parts. Although RPM makes both Testor’s Model Master Acryl AND Polly Scale, they are different in formula and not all that happy with each other, in more or less equal proportions.



First Wash

After soaking up extra and a drybrush with black

You can super-dilute water/alcohol based paint and use it as a wash, just like oil-based paint. The increased surface tension of the water means it doesn’t spread as easily as oil-based paint, and tends to bead up. Use a tiny hint of dish detergent, or watch it and brush it out as it dries. I’ve had very nice results using metalic and/or black washes over brown airplane engine exhausts, dark color washes to suggest depth. Unlike oil paint, when its dry, it won’t come up again, so you can’t do the “sludge” wash to and then clean off the excess for panel lines and the like. On the other hand, with water based paint, you can just blot it up with a damp tissue, paper towel, sponge, etc, if you don’t like how it looks.

Here’s links into my Flickr photo collection:

4 responses to “Thinning, mixing, spraying and ‘washing’ with water-based model paints

  1. Old and gray as I am, I still have to find a way of effectively removing an applied paint without causing catastrophic damage to the underlying plastic sho rt of sanding until all detail has been obliterated

  2. Hi Nick,
    Three suggestions:
    1) There is a pale green liquid paint remover sold in the model railroad section of your local hobby shop that certainly removes Testor’s gloss spray paints. That’s what I used my bottle on, and it worked great. Soak a bit, then apply an old toothbrosh and watch the old paint fall off. Afrter filtering out the old paint, the liquid looked perfectly re-usable. Probably it has a lifetime but I was impressed. Model Railroad people buy painted stuff and strip it all the time, so it seems like a natural. I used gloves when doing this and recomend eye protection as well. I wear glasses.

    1.1) There are also orange/citrus oil-based paint strippers now on the market, and I’ve got some and I’ll test it out.Should be just the stuff- bust up the dried enamel paint but not harm the plastic.

    2) I have been told that oven cleaner (lye I’d expect) does a similar job. I believe it. FOR SURE I’d use gloves and eye protection… I might do the deed IN a heavy plastic bag too. Can’t be too safe with Lye.

    3) I have used Windex amonia-based glass cleaner to strip Future floor wax (aka Kleer) with great success. I’ve also seen it attack Gunze Sangyo acrylic paint and I’d expect you could strip it with any household amonia. The stuff never really seems to dry, to me, so its not completely surprising it comes off easy.
    – Along this same line, Tamiya make a thinner for their acrylic paint that’s some interesting alcohols and it will remove dry paint.
    – And I’m told denatured (ethyl) alcohol will strip Polly Scale acrylic, which I’ve tested on small scale and been reasonably happy with.
    – And finally, comon paint thinner may remove straight oil-based enamel paint. No need for the extreme paint strippers or removers. Just some thinner, a plastic bag, some old tooth brushes. I’d probably close the bag and work *through* it.

    So there are three steps to try before sanding. And I have to say, having sanded more than one paint coat off, or at least down, that wet dry paper in high numbers, with plenty of water, and a flat surface, isn’t the worst thing I’ve ever done to a model. I wouldn’t care to make a practice out of it, but for whatever reason you want paint off (wrong color, build-up or unwanted texture) a careful wet-dry pass can be the basis of a fairly good final coat. You’ll lose rivets and raised details, of course. But paint is usually softer than plastic, and the big problem I’ve had sanding it off is the build-up in my sanding medium. Hence wet dry and lots of water.

    I guess I ought to paint something and then strip it :^)

  3. All I want is A web site to go to to show me if I enter different colors what will the final color look like. Based on ratios and not based on brands but thats ok too. I build plastic models.

  4. Boy oh boy I’d love that too. In Openoffice Draw and no doubt other programs, there’s a meny to change colors, which offers-0-255 values for Red, Green and Blue color in youro display.
    If you have the patience to learn it, this is a good way to test basic color blends. But you’d have to lguess at Red, Green and Blue values, at least to start.

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