Tech Tips - Painting

Choosing Airbrush Features

Tips for Cleaning Your Airbrush

• 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.

To prime or not to prime is a complicated subject. This section has to do with painting metal.

Being a model railroader myself, one of our biggest challenges is painting brass models.  Brass or not, many of the challenges of painting brass are applicable to other metals.  Simply stated, the problem with painting brass is the oxidation that accumulates on the surface immediately after any surface preparation.  The more time for oxidation, the less chance you have for adhering your paint.  

A brass model will usually have a finish color and a lacquer finish.  If you plan to remove the lacquer, a strong paint remover works well.  For early models that do not have this finish, you will often have dark areas of the model where people have touched the brass and left oils, salt, and acids which enhanced the oxidation of the brass.  We typically would just say these models were badly tarnished.  Tarnish to brass is like rust to steel.  To have a successful paint job for both, one has to remove all oxidation.  The easiest solution is sandblast.  Although this sounds difficult the equipment isn't very expensive if you already have an air compressor for painting.  One can get a simple sandblasting nozzle and gun from Harbor Freight for around $20 - https://www.harborfreight.com/21-oz-hopper-gravity-feed-spot-blaster-gun-95793.html.   I get my sand from Lowes or Home Depot for a couple of bucks.  You'll want to sieve the cheap sand because is has some larger sized particles that can clog the sandblasting nozzle.  

Now that you have exposed metal, the goal is to get the surface cleaned as quickly as possible and minimize the exposure to air.  My technique is to wash the parts with window cleaner in a large pan so all the items can remain submerged until the final rinse.  If you really want a superior binding paint job, the professionals add one more rinse with a chemical preparation.  To prepare a metal surface for painting, one really needs to use a chemical prep.  Now days with the internet, one can find all different types and for different prices.  One I used in the past was a prep for aluminum which an auto body shop guy had sold me.  There were two components, a wash and a rinse.  The stuff worked great, and would even turn the brass a slightly pink color.  I wasn't sure what the stuff was, and this in the days before MSDS information.  After learning more in college, my guess, it was a weak acid and the rinse was a neutralizer.  I have seen similar things now on the internet, but they all cost money.  As a substitute to having to buy something special, a number of modelers recommended using vinegar.  I started using vinegar and I like the cost and results.  I would still get the pink tone to the brass but not to the magnitude that would appear with the commercially available chemical washes.  Again, all the parts need to stay submerged until you are ready to dry and paint.

The next step is an option and depends on the size of your project.  Keep in mind the oxidation starts as soon as the brass is exposed to air.  That means oxidation is building all the time that the items are drying.  If I have a lot of parts, I use a hair dryer and dry them the best I can.  Then line them up and give them a quick coat of flat Rustoleum.  I focus on the surface that will be exposed or handled.  The coverage doesn't have to be complete, just a film to block the oxidation.  I also do this step if the parts have multiple colors and need protected until painting the final color.  There are a number of risks when spraying oil based paints from an aerosol can.  You can chase a drop of moisture out from a crack that blemishes the oil painted surface, and spraying from an aerosol can can be tricky.  You'll also want to wait a few days while the model bakes to completely cure the oil based paint.  

However, if you have a well prepared surface without any oxidation, you can proceed to painting with Modelers Paint without the primer coat.  Our paint will bond extremely well to any cleaned surface.  In addition, the glues we use in the paint can be baked which will give you that same feel that the old oil based paints of Floquil and Scalecoat used to provide.  One other advantage, because Modelers Paint is water based, a slight film of moisture is not a show stopper.  I take my model from the wash pan, blow it off with the airbrush, and then use the double action feature of the airbrush to spray a rinse of 91% alcohol over the model.  The alcohol captures any large drops of moisture, and the drops are blown away with the air from the airbrush.  The process is quick and thus minimizes the time the metal is exposed to air.  Once rinsed, you can begin painting and don't need to worry about moisture.   

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)
• Or snip the end off of the whip attachment, leaving prongs about 1 1/8" long, pinch together to insert into bottle
• Add a few drops of Isopropyl alcohol to paint to enhance mixing
• Move attachment around inside of paint bottle (CAUTION: Spinning the mixer too fast will result in paint flowing over the sides of 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.

• Use the split-stick attachment and submerge the tip in the paint (our paint bottles are over-sized to allow space for mixing)
• Or snip the end off of the whip attachment, leaving prongs about 1 1/8" long, pinch together to insert into bottle
• Add a few drops of Isopropyl alcohol to paint to enhance mixing
• Move attachment around inside of paint bottle (CAUTION: Spinning the mixer too fast will result in paint flowing over the sides of the bottle.) 

• 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.

We do not carry a primer for use with our paint but I can give you some suggestions to consider depending on the reason you need a primer. If you want to paint on metal (not plastic) and desire to add some tooth to the surface, I recommend the use of a flat Rustoleum spray paint; this also minimizes the need for extensive prep work. 

Typically I do not use a primer on other types of surfaces unless I am painting over dark or unevenly colored surfaces. To cover these types of surfaces, I first spray a base coat of ModelersDP paint in white or gray. Most other primers would also be compatible with ModelersDP paint.

ModelersDP paint is airbrush ready and therefore quite thin. What works for me is to pour a little paint onto a pallet, let some time pass so the alcohol evaporates and leaves a little thicker consistency of pigments in the paint mixture. You should have success brushing your paint into those tight areas.

Interestingly, ModelersDP paints started with the concept of washes for weathering and then we realized how easy the paint was to airbrush.  Our goal was to have a carrier that would flash off quickly yet have great properties to spread the pigments of the paint. Thus, we use Isopropyl alcohol 91% which has some great properties for smoothing paint. 

The down side, washes and airbrush paints are diluted to a point that spreads the layer of paint pigments a little too thin when brushed.  To accommodate, I just use a small plastic paint palette, pour a little airbrush paint into one of the cups, and let some of the alcohol evaporate before brushing on the paint.  If the paint starts to dry on the palette, I dip the brush in a little alcohol and mix in with the paint.  The process works if you are using say a red over an orange, but a yellow over green....  you might be applying a lot of coats to achieve opacity.

One of the great things about this paint is that it can be diluted as much as needed using Isopropyl alcohol -- although I have not made dirty windows, I have done a lot of other types of dirtying up. I would suggest starting with a very diluted paint (like 5% paint, 95% alcohol) in your airbrush, hit the windows with a layer -- there will be a nice mist coming from your airbrush at this ratio, let the alcohol dry and see if its dirty enough.  With this paint, you can dilute it to spray a thin film of color or apply enough passes to get a completely opaque finish.

As for thinning, that is an easy question -- use simple and inexpensive Isopropyl alcohol, 91 percent.  If you don't have any, Walmart is usually the cheapest, but Target and all the drug stores carry it.  

 I also suggest rinsing your airbrush, paint pot, and nozzle with water, and then rinsing with Isopropyl alcohol.  These steps remove any dust or other contaminants.

As for the ratio of thinner to paint, just about any ratio works.  However, if things are not working as expected, the secret is to dilute your paint, and if that doesn't solve the problem, dilute some more.  The benefits of diluting are ease in mixing the paint, a smoother finished surface, a nice uniform fog or mist of color.  The downside and because the particles of paint are being applied slower, one has to spend more time painting, allow time for the alcohol to evaporate, move the spray around on the surface of the model more slowly, and slowly build up the layers of paint particles in multiple passes of the airbrush.  Bottom line, thinning is a balance between a person's desire to get the project done and the expectations of a satisfactory result.

There are many factors to consider when determining the thinning ratio.  On one end of the spectrum when you want an opaque color, you can use the paint right from the bottle.  The other end of the spectrum is weathering when one wants just a light fog or mist of a color.  You can dilute 95% alcohol to 5% paint.  When I weather, my paint is so diluted one can't tell there is color being sprayed.

For ultimate airbrushing success, ModelersDP paint needs to be mixed very well. A mechanical mixer is best.  If you just shake the bottle and your arms (both arms) get tired, you are only about one quarter of the way mixed.  If the paint has sat for a time, the paint particles settle out of the solution and really need some strong agitation to disperse again.  Before mixing, a little alcohol to freshen the mix helps to break up the polar and molecular attraction between the different paint components within the bottle.  The goal is to get everything back into solution.  Filtering your paint will still get you satisfactory results, but you will just be wasting some of the paint on the filter.

Acrylic paint is truly a blessing when it comes to clean-up.  Clean-up is so easy with just a water rinse and a quick spray of window cleaner (ammonia based) -- is really the component that is active.  In quantity, ammonia agitates all the alcohol and paint particles by putting them into solution.  One needs to rinse the window cleaner from the airbrush or model with water, and I recommend a final spray rinse of alcohol.  Even a molecule or two of ammonia left on the surface of the model or in the airbrush is a contaminant that reactivates in the presence of water.  You will see the result of ammonia, oil, or other similar contaminates as a small spec where the paint is repelled on the surface of the model.  Not to worry, if you get a paint blemish, lightly blow some air on the spot until the sheen on the surface is gone.  You can then lightly begin applying paint, but not to the point where the paint becomes dispelled from the spot.  The process is repeated until the blemish can be covered.  

We recommend using a mechanical mixer. We sell an inexpensive mini mixer on our website that works great for our bottles. Here are my tips:

• Use the split-stick attachment and submerge the tip in the paint (our paint bottles are over-sized to allow space for mixing)

• Or snip the end off of the whip attachment, leaving prongs about 1 1/8" long, pinch together to insert into bottle

• Add a few drops of Isopropyl alcohol to paint to enhance mixing

• Move attachment around inside of paint bottle (CAUTION: Spinning the mixer too fast will result in paint flowing over the sides of the bottle.)