Tuesday, 07 August 2007 04:33

Using Artist Acrylic Paints for Rocketry

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I enjoy painting plastic models and pewter miniatures used in games. I've used many different kinds of paints, so when it came time to paint another rocket, I decided to try some of them, rather than another can of Krylon. I've settled on using artist grade acrylics for my miniatures, so I decided to start there.

I chose acrylics for a variety of reasons. Typically they are non-toxic, they clean up with soap and water, can be thinned with water, are permanent, durable, and are readily available.

I purchase most of them from either Robert's or Michael's craft stores (don't forget the 40% off coupons in the Sunday newspapers).

The brand I like best is Liquitex, but I have had good luck with Golden and Winsor & Newton. The Liquitex paints come in a little wider color range, and are a little cheaper. Experiment yourself and see what works best! The model acrylic paints (like Testor's Model Master Acryl line) do come in a wider range of colors and are already thinned, but they seem fragile-any little scratch seems to take them right off.

Most of the artist paints can be heat-treated to improve their durability. Usually baking them at 200 F for about 30 minutes works, however, my wife would not appreciate an Alpha in the oven, so I put them on the dash of my car, and park in the sun.

Acrylic paints consist of two parts: a pigment and a binder. Usually the pigment is a naturally occurring mineral that is finely ground, and the binder is a plastic resin. Most artist acrylic paints across brands are compatible, but not all. Some very interesting colors can be mixed together. Get a color wheel and experiment. Also, there are a wide variety of pearl colors, or interference colors. Pearl colors appear as metallics, and interference colors change color depending on the angle you look at them

Make sure to buy the artist-grade, and not the student-grade paint. The student-grade paints are about 2/3 the price, but have less pigment in them, and come in fewer colors.

These paints have different viscosities between brands, and even between lines in the brand. High-viscosity paints have almost a peanut butter type consistency, and need large amounts of thinning for our purposes. The lower viscosity paints typically have the same amount of pigment as their high-viscosity counterparts, but need less thinning, so they go further. I use the medium-viscosity Liquitex, or Golden's Most of these paints have 2 ratings on them: Lightfastness and Opaqueness. Lightfastness refers to the pigment's ability to withstand fading. The highest grade of Lightfastness means the paint will stay it's original color for 100 years when exposed to museum-quality lighting. Most paints fall into this category, however many of the fluorescent colors shouldn't be used-they will break down in a few days of outdoor light.

To thin these paints, a variety of items can be used. Water is the most common, but don't use too much. As the water dries, the paint shrinks, and can crack. Add a drop or two of dishwashing detergent to the water to lower the surface tension. Windshield wiper fluid is another thinning agent, however I have had the alcohol react with the plastic binder in a few brands. Do not use mineral spirits or turpentine! Unfortunately, the best thinner for acrylics is not the cheapest--mediums. Mediums are sold for different types of thinning, from brushing to airbrushing, to giving a very glossy or dull finish without any overcoat. Most mediums are the plastic resin in a nonvolatile suspension. One thing I have learned, is to use the same brand of medium for the paint - different resins can react with each other. You can use several mediums, like combining airbrush medium with gloss medium. As a rule of thumb, do not user more than 25% medium in the paint. Try thinning to different levels, but remember, it is easier to thin the paint more than thicken it back up. A little medium goes a long ways.

I have applied these paints using brushes, rollers, and airbrushes. The best results have been with an airbrush, although a roller or brush can be used equally well with a few cautions. For brushing, use the highest quality, softest, synthetic fiber bristle you can find. Natural bristles tend to absorb the moisture in the paint, so it doesn't dry naturally, and can crack. Softer bristles leave less of a brush mark. Don't skimp on a quality brush, you wil thank yourself later.

If you don't have access to an airbrush, a spray bottle (like the kind for misting plants) can work too. Find the finest spray pattern you can, the finer the spray, the more uniform the paint will be. Pump-style hairspray bottles can work, but very little paint will go down per pump. Even though the paints are labeled non-toxic, I would still recommend using a NIOSH approved paint mask for any airbrush work. To use this paint in an airbrush, thin the paint to the consistency of heavy cream. Set your air pressure to about 20-23 lbs., and hold the airbrush as perpendicular to the rocket as possible. Start the spray before the rocket, and use a smooth stroke, ending the spray after the rocket. I practice on an old piece of cardboard, so that I can get the color and consistency that I want.

If you have spirals in the body tube to fill, I've used a product called Gesso with some success. Gesso is used to prime canvas for acrylic or oil paints, so that the paint does not soak through the canvas. It looks like a thick, syrupy material. I thinned it using water, then applied it using a brush directly onto the spirals. I had to let it sit overnight for complete drying, though. After that, I sanded the Gesso smooth. You can apply masking tape about 1/16" from each side of the seam, to make a guide if you like. It may take more than one coat, try to apply thin coats. If you want to use a primer, I've used whatever I had handy-spray cans of Krylon, airbrushing model paint primer, or an acrylic primer made by Designs From the Heart, or thinned Gesso. Each seemed to work equally well, but I let the oil-based primers dry for about 48 hours before I tried to apply acrylics over them. The solvents in the primer should be completely outgassed, or the paint will bubble later.

As a top coat, I have used either Liquitex's Solvar gloss varnish, the Gloss medium, Future floor wax, or simply left it alone. Some of the paints leave a little rough surface, and do need topcoating. Future has worked well, and it is cheap. The varnishes are a little on the expensive side, but very durable. Solvar is also removable with turpentine, so you can repair the paint easily. Solvar also has some UV inhibitors in it, which helps the paint resist fading.

Liquitex has a website with good technical information at www.liquitex.com. Golden's is www.goldenpaints.com. Winsor & Newton's website is www.winsornewton.com, but it seemed to concentrate more on their oil paints. Each has technical contact email, which I have found to be fast, friendly and expert advice (Liquitex put me in contact with their chemical engineer when I had a question on heat curing!). Acrylics have been a good alternative for me. They are more versatile, cheaper, easier to use than oil based enamels, and I because of their non-toxic nature, I can paint inside my house with them. Experiment with them, and see if they work for you.

Have fun, and keep the pointy end up! This article originally appeared in the December, 2002 issue of the Ballistic Beehive.

Read 11136 times Last modified on Friday, 03 February 2017 17:03

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