Tech Tips - Painting

There are several types of airbrushes and a sizable price spread.  You don’t need to spend a lot of money to enjoy the art of airbrushing, but there are a couple of important features that will make your painting experience most enjoyable. 

Read the sections below for feature recommendations.

For best success with acrylic paints, the dual action, or sometimes called double action, airbrush is a must.  Acrylic paints tend to dry less quickly than solvent paints.  With the dual action airbrush, you can easily back off on the volume of paint while maintaining the flow of air.  This process allows the paint to dry and minimizes the potential for runs.

The airbrush quick-connect, or sometimes called quick-disconnect or quick-release, is a handy device that attaches between your airbrush and supply hose.  Instead of having to unscrew the airbrush, the quick-connect releases the airbrush by simply pulling down on a ring.  When the airbrush is released, the airline is closed, thus maintaining the pressure in the supply hose.

With a gravity flow airbrush, the paint cup sits on top of the airbrush, and paint-flow is accomplished by gravity. There are minimal parts through which the paint must pass before being mixed with the air.  Thus, you have fewer places for the paint to accumulate, dry, come loose, and then clog your airbrush.  

A typical 7 cc cup on a gravity flow airbrush is plenty of paint to cover an HO train car.

Some artists prefer the siphon type airbrush, where the cup or bottle is below the airbrush.  The benefit of a siphon airbrush is that it allows the user the ability to sight along the top of the airbrush and aim the paint at a very precise location. For weathering, pin point location might be a plus, but for general coverage, a gravity flow air brush works great and minimizes cleanup.

The cup or bottle on the siphon type airbrush typically holds more paint than the gravity flow cup which may be beneficial with some projects.

The tip size on your airbrush is a matter of preference. 

• ·  Small tip, 0.2 mm, for very fine work, minimizes flow of paint
  
• ·      Mid-size tip, 0.3, more coverage per pass
  
• ·      Larger tip, 0.5, increases coverage, increases risk of paint runs
  

LEARN MORE: The small tip, such as a 0.2 mm, is for very fine work and minimizes the amount of paint passing through the airbrush and onto your model.  The small tip is great for highlighting a model and lowers the possibility of having your paint run.  On the downside, you will not be covering much area per pass thus painting an entire HO car could take about twice the time as using a 0.3 mm tip.  

To speed the painting process, you might want to consider the 0.5 mm tip, but now you will be putting on quite a layer of paint per pass of the air brush which will increase your chances of having your paint run.  Not to worry, with practice, a dual action airbrush, and the forgiving nature of ModelersDP Acrylic Airbrush Paint, you will be painting like a pro in no time. 

• Prep your item to be painted with a quick wash of window cleaner.
  
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• Follow the spray wash with a water rinse. Use a container to catch any pieces that might come loose. 
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• A quick rinse under the tap finishes the process of prepping. Again, try to catch the rinse water just in case a piece of the model becomes dislodged.
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• Double action airbrushes are easy to use as a blower for drying your model and blowing water out of small hidden corners.
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• Always test the model and prior painted surfaces for any reaction to alcohol.
• A little alcohol can be used to displace the water and shorten dry time.
• Some painted models will weather nicely with an alcohol wash.
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• A wash bottle simplifies distribution of the alcohol.
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Learn More: Model manufacturers use a releasing agent during production.  The agent remains on the plastic model unless washed and will result in a poor bond when using acrylic paints.  An easy solution to the problem is spraying the surface of the model to be painted with an ammonia-based window cleaner such as Windex®.  Apply a little agitation by swishing the model in a bucket full of water.  The bucket is recommended as it will catch any small part that might come loose and fall off the model.  The bucket wash is followed by rinsing the model under tap water, but again, it is recommended to catch the water in a bucket just in case a part is dislodged.

If you are in a hurry to paint, you can use your airbrush as an air blower and gently blow the water droplets off the model.  Using a little 91 percent alcohol in the airbrush cup can also aid in cleaning the surface, displacing the water droplets, and evaporating the moisture much faster than air alone.  The surface should be free of visible water but does not need to be moisture free -- one big advantage to airbrushing with acrylic paints.

ModelersDP paint has been formulated with surfactants for ease in mixing. If you have primarily used solvent-based paints, you might find mixing acrylic paints will take a little more time. 

For best results, mixing with a hand held mechanical mini mixer is highly recommended to distribute the particles of paint throughout the alcohol carrier:

• Use the split-stick attachment and submerge the tip in the paint (our paint bottles are over-sized to allow space for mixing)
  
• Tap the ‘On’ button for each count of 1 to 100 (CAUTION: Spinning the mixer too fast will result in paint flowing over the sides of the bottle.)
  
•  Move stick around bottom of paint bottle, approximately 5 counts per rotation
  

NOTE: Use of the mixer will result in better pigment distribution than shaking the bottle. 

**the handheld cordless mini mixer sold by ModelersDP is available on the website for $5.95

LEARN MORE: Acrylic paints are comprised of solid pigment particles, additives for disbursement of solids, bonding agents, and fluids used as carriers.  At the molecular level, the characteristics of the fluids in acrylic water-based paint typically repel the pigments.   To assist in rectifying the problem, special polymers and surface energy inhibitors are added to ModelersDP paints, making the surface of the pigments hydrophilic. Thus, once the solid particles are well mixed back into the carrier, ModelersDP acrylic paint behaves similarly to a solvent-based paint.

Strain your paint if

• ·       you see evidence of crusting on the inside of the bottle
  
• ·       paint has a layer of ‘skin’ on top
  
• ·       airbrush unexpectedly clogs
  
• ·       small splatter spots appear beyond normal path of airbrush spray line
  

How to strain your paint

• ModelersDP sells disposable filters that can be reused if cleaned after use.

• Filtering is not necessary but is recommended for that perfect paint job.
•  Hold the filter over airbrush paint cup
• Pour paint into the bottom of the filter 
• Filtered paint will drain into airbrush cup
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• Turret tops make for easy and efficient pouring (available on ModelersDP website).

• Filters can last a long time if cleaned with window cleaner, rinsed in water, and allowed to dry.
  
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• ·       For great results, use ModelersDP 190-micron Disposable Paper Filters
  

LEARN MORE: ModelersDP paint is strained just before bottling so if you are pouring only a small amount of paint from a new bottle, you should have good results. However, after the paint sits for a while, there is a chance that the pigments would rather clump together than be suspended in the fluid carrier. Use of the Deluxe Cordless Mini Mixer, sold by ModelersDP, will easily break down these clumps, which may eliminate the need to strain your paint.  Bottles of paint that have been opened, have sat for a while, have any evidence of crusting on the inside of the bottle, or are skimmed over should be strained.

While spraying, you can tell if your paint needs straining when the airbrush unexpectedly clogs or small splatter spots show up beyond the normal path of your spray line.  If you are diluting ModelersDP paint for a light weathering effect on your finished model, straining is highly recommended.

Experienced professional painters who use acrylic paints strain their paint each day before use.  Therefore, to minimize splattering and to get the smoothest finish possible, consider straining your paint. With ModelersDP 190-micron Disposable Paper Filters straining is a snap.  Simply hold the filter over the airbrush paint cup while slowly pouring into the bottom of the filter, thus minimizing the paint coverage on the filter and loss of paint.

If paint has not been used in a while, the pigments and other materials will separate.  This separation is normal but can sometimes be difficult to get blended together again. Here are suggestions for getting your paint successfully mixed:

• ·        Try adding a few drops of fresh alcohol before mixing

• ·       Use a mechanical mixer to stir the paint inside the bottle. Modelers sells a mini mixer that comes with multiple attachments.

• With the mixer attachment inside the bottle, gently and quickly tap the switch on and off; CAUTION – spinning the mixer too fast will cause a full bottle of paint to overrun the top of the bottle. Tapping the switch or using short bursts is best practice for full bottles. 

o   Stick attachment: used for basic stirring of fresh paint

o   Whip attachment: this attachment can be slightly altered to fit inside the paint bottle.  Using nippers, clip off the two looped wires at the very bottom of the whip, leaving four 'prongs'. This allows the clipped wires to offset and be pinched together for insertion into the bottle. The whip will expand once inside the bottle and can very effectively mix the paint.

• Just about any air pressure will work with ModelersDP acrylic airbrush paints. Pressures from 10 PSI (pounds per square inch) to 60 PSI are possible.
  
• ·       Low pressures are best for very fine lines of paint
  
• ·       High pressures are for atomizing the paint and increasing the rate of coverage)
  
• ·       25 PSI is a good starting point from which to experiment

• ModelersDP paint is very forgiving and a blemish or run will often smooth out as the paint dries.  For a blemish or run that needs erased:
  
• ·       While paint is still tacky, spray surface with an ammonia-based window cleaner
  
• ·       Swish the model in a bucket full of water (this will catch any small part that might come loose)
  
• ·       Follow by rinsing the model under tap water (again, use a bucket just in case a part is dislodged)
  
• ·       Allow to dry; model should be free of droplets and visible water
  
• ·       Optional: Use airbrush to gently blow the water droplets off the model
  

LEARN MORE: ModelersDP paint is very forgiving.  If you do happen to have a run or you see a buildup of paint in a localize area, not to worry.  With the extremely fine particles of pigment and fluid dyes, ModelersDP paint will often smooth out while drying.  A second application will often hide the mistake.  If you have a blemish or run that needs erased, here’s another advantage of ModelersDP water-based acrylic paint.  While the paint is still tacky, spray the newly painted surface with an ammonia-based window cleaner and prep the model as if you were preparing your model for the first time (See Model Preparation topic).  

To apply an opaque finish to your model-

• ·       Apply paint in light layers
  
• ·       Allow surface moisture to disappear between coats
  
• ·       Continue layers of paint until desired opacity is achieved

LEARN MORE: If your goal is an opaque finish it is best to apply layers of paint; this is especially true when painting plastic surfaces.  A simple technique is to provide ‘tooth’ to the surface of your model by first spraying a very light coat of paint over the surface.  Because the initial layer is very light, the carrier evaporates quickly leaving a slightly tacky surface.  The tacky surface is created by the bonding agents in ModelersDP paint. Each sequential pass can be a little heavier until you achieve your desired opaque finish.  

ModelersDP paint has been blended with binding agents that react with air once the carrier has evaporated. As the drying takes place, the particles of pigment become attracted to the plastic surface and to each other. The bonding agents minimize the chance of paint runs and results in an exceptionally smooth surface. 

Because the pigments in ModelersDP paint are so fine, spraying in one location until you see the surface color change could lead to runs.  The best method is to watch for sheen to appear on your model and stop your spray. The sheen evaporates quickly, and you are ready for an additional application of ModelersDP paint.

Repeat this method of light coats until you have achieved the desired opacity. When applying multiple layers of paint to create an opaque covering, you will notice the wet paint has an egg shell texture.  But not to worry, ModelersDP Acrylic Airbrush Paint will dry extremely smooth. 

• Prep your item as described in Model Preparation.
• Stir and strain paint, also described above.

• For weathering, dilute paint at a ratio of 5-10 percent paint to 95-90 percent alcohol. Over diluting is not a problem, your project will just take a little longer.
• Pour a little paint in the bottom of the airbrush bowl. Fill the remainder of the bowl with alcohol.
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• Mixing the paint and alcohol is simple by using your gravity flow airbrush. 
• Place your finger over the end of the airbrush, push down on the air release, and SLOWLY pull back on the trigger. CAUTION: Too much air rushing into the bowl will blow paint up and out of the bowl.
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• Always test the airbrush and paint mixture before spraying directly on the model. Just a piece of paper pinned to a cardboard box/paint booth is easy, inexpensive, and practical.
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• Using low air pressure, you can get very close to the model and easily spray between the outer braces.
  
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• Apply darker colors first, then highlight with lighter colors to accentuate the hidden details of the model.
  
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ModelersDP Weathering Collection includes some of our favorite weathering shades.

• No need to waste your diluted paint - if you have only a small amount left in the bowl, you can easily add it back to the bottle with the aid of a small funnel. 
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• Purchase ModelersDP Mini Funnel in Paint Accessories

• Clean-up is quick and easy. A couple of squirts of ammonia based window cleaner followed by a tap water rinse does the trick.
  
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• Always use a plug in the sink, just in case you drop a small part.

• ·       Dries to the touch in about 20 minutes 
  
• ·       After allowing the surface to dry for 24 hours, you should be able to apply masking tapes 
  
• ·       Wait 2-3 days before applying decals  
  
• ·       Paint continues to cure over time
  
• ·       For an extremely durable finish on glass or metals, bake painted object  at 250°F for 24 hours
  

• ·       Lightly spray airbrush cup with ammonia-based window cleaner
  
• ·       Rinse the cup
  
• ·       Use the window cleaner and a tooth brush to clean tip; pull needle back when cleaning tip
  
• ·       Add a small amount of window cleaner to cup
  
• ·       Circulate cleaner through the airbrush, under pressure (there is some discussion about whether ammonia should be used to clean the airbrush -- although we have not found it to be a problem, circulating alcohol instead is also effective).
  
• ·       Follow with a rinse of tap water and/or alcohol 
  

In looking over the internet, you will find a variety of options for both airbrushes and assorted tips.  Typically, you’ll want a smaller tip for painting miniatures, but that is only part of the story.  

For a dual (double) action airbrush, the shape of the needle and its seat in the nozzle will play a major role in how the paint is released from the airbrush.  

In painting miniatures, you are looking to use low quantities of paint, to minimize the cone pattern of paint spray, and to easily control the rate at which the paint flows from the airbrush.  The low quantity of paint can be achieved with a small nozzle size, say in the range of 0.2 or 0.3 millimeters.  

What doesn’t get much discussion, but is very important, is how to control the cone pattern of spray and flow of paint. See the next section, Controlling the Cone Spray.

The cone spray pattern flowing from your airbrush is controlled by nozzle size, needle taper, needle and nozzle cap, air pressure, distance between the airbrush and the surface being painted, and the consistency of your paint.  

The smaller the cone spray pattern, the greater chance for success when painting miniatures. See sections on Nozzle Size, Needle Taper, and Needle and Nozzle Cap.

Calipers can be used to measure the needle at the nozzle.

A smaller nozzle restricts the amount of paint that can be discharged from your airbrush.  Although a lot of attention is given to the nozzle size, other factors can play just as important a role in successfully painting miniatures.  Starting with a small nozzle tip, you can enhance your chances for success when painting miniatures.

Determining the nozzle size on your airbrush can easily be accomplished by measuring the needle with calipers. 

• Loosen the needle chuck and confirm the needle is snugly seated inside the nozzle, then re-tighten the needle chuck.  
• Remove the needle and nozzle cap to expose the needle protruding from the nozzle.  
• Being careful not to damage the point of the needle, slide the calipers down that portion of the needle that is exposed beyond the nozzle.  
• With the calipers gently resting against the nozzle, measure the diameter of the needle.  Typically, you will want to read your calipers in millimeters. 
  

As you reassemble your airbrush, make sure the nozzle cap is correctly sized to the nozzle.  You should see a small uniform gap around the nozzle and feel a nice uniform flow of air when the trigger is pressed.  

Your airbrush might have a small “O” ring to seal around the bottom of the nozzle cap.  Over- tightening the nozzle cap can damage the “O” ring and allow the nozzle cap to seat down on the nozzle, thus restricting the air flow.  Properly seated, the nozzle should be flush to the top of the nozzle cap or just barely extend beyond the cap.  

In a dual (double) action airbrush, the throw of the trigger and the needle taper will control the flow of paint from the airbrush.  Greater taper to the needle will give less flow of paint and better control for painting miniatures.

Manufacturers provide airbrushes for a wide variety of uses, but in order to meet most customers’ needs, the nozzle and needle are sized to provide a typical conical spray pattern of about 1 inch in width.  The standard nozzle size might range from 0.3 mm to 0.4 mm, and the taper of the needle varies among manufacturers.

For painting miniatures, needles with less taper will provide greater control of your paint flow and better control to create a small diameter cone spray.

When painting miniatures, the taper of the needle actually plays a more important role in controlling the flow of paint than the size of the nozzle.  You can think of the needle and nozzle as a valve.  When the needle is fully inserted into the nozzle, the flow of paint is blocked and the valve is closed.  As the trigger is pulled back on a double action airbrush, the needle recedes from the nozzle and the valve begins to open.  As the trigger is moved back and the needle moves away from the nozzle, needles with a greater angle of taper will allow more paint to flow than a needle with less taper.  

To determine the taper of the needle, you can measure the needle diameter with calipers and determine the distance from the point of the needle to where the needle first begins to taper.  With a little trigonometry and knowing the diameter and length of taper, one can determine the angle of taper.  A smaller angle will result in less paint and easier control.

The nozzle cap is sized to the needle.  The needle cap can be removed, which will extend the length of the stream before becoming a more conical spray pattern. The pictures below show the airbrush with the trigger engaged at quarter, half, and full pull or throw.  You can see the fine line protruding from the airbrush and then the conical spray pattern begins just a few millimeters beyond the nozzle cap.

When testing an airbrush, always check that a nice flow of air is allowed to pass around the end of the nozzle.  As mentioned above, the nozzle cap needs to be sized to the nozzle.  An easy check is to look for a small gap between the nozzle and nozzle cap and then to test the airbrush using a little alcohol or water.  Holding the airbrush next to a light source will allow one to see the airbrush in action.  

Increased air pressure will move the start of the conical spray away from the nozzle and increase the quantity of paint coming from the airbrush.  The high pressure creates more vacuum around the nozzle.

The greater the distance between the airbrush and the surface being painted, the greater the diameter of the conical spray.

Thinned paint will allow easier flow of the paint through the nozzle, therefore the trigger doesn’t need to be pulled back as far and the jet stream will extend farther from the airbrush.  Thus, a fine paint line is created farther from the airbrush.