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Scale model. Modelling masterclass. Prepering for paint. Part 2

23 Dec
2011

Using an airbrush is like writing – everyone’s style and technique is slightly different. In order to develop yours, practice, practice, practice. Begin by choosing an easy fluid that does not need complex mixing and is easily cleaned, such as ink or food colouring and practice on paper or plastic card.

Before you start using paints, I suggest you begin your airbrush apprenticeship by using a little colouring agent such as food colouring in the airbrush (Photo 1). Then, even before the first ‘squirt’, think about the following points.

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If you have an airbrush with psi calibration, I recommend starting with low pressure, 12-15 pounds per square inch. (A useful tip on pressure gleaned from my own experience is that it shouldn’t be necessary to use more than 25 psi for painting models and only go over 20 psi if you are painting a large area and need to move quickly in order to prevent the working edge from drying out.) If you are like most modellers and own a single-action airbrush (Photo 2), start by fully closing the needle so that no fluid can escape. Then open the needle a fraction and gently push the trigger to release a small quantity of fluid in the direction of your paper. If no colour appears, open the needle a fraction more and try again. By opening and closing the needle you begin to see how the flow of fluid can be controlled (Photo 3).

Drawing and joining the dots

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Now start having some fun – draw lines across your page. Doesn’t sound like much fun, but while you are learning aim for a clean line as if you were writing with a biro. If you get a spotted or grainy effect at the edge of your line, you need to increase the air pressure out of the airbrush by using the trigger as described in your manual. If the fluid is wet and ‘spiders’ away form the nozzle, you have too much colouring agent and too much pressure (Photo 4). Once you have the pressure/fluid flow correct, try pulling the airbrush away from the page and opening the needle further, to increase coverage. Practice making dots, then joining them together with a fine line, a fat line and then tapered lines. You are aiming to get a smooth edge to your coloured area. The purpose of all this practice is to put you in control of your airbrush, to give you confidence and to begin your enjoyment of your new technique. Even the cheapest airbrush should be capable of producing fine lines when the pressure is correctly adjusted. When you are comfortable and achieving what you set out to achieve, you can start using paints, but first thoroughly clean your ‘brush.

Cleaning

Inks and food colouring are easily flushed through the airbrush with water. First empty any excess colouring agent back to its pot, then take out the worst of any residue by brushing the colour cup with a bristle brush (the type used for oil painting). Rinse the airbrush thoroughly with a thinner compatible with the colouring agent until no trace of colour can be seen when the fluid is forced into a clean tissue. Stopping and restarting the airflow will agitate and remove stubborn traces. This cleaning technique is usually enough between colour changes, but at the end of the session or between different types of colouring agent (eg enamels to inks) it is necessary to be more thorough (Photo5). With acrylics I use an ‘active foamer’ and for enamels a liquid reamer. The latter is xylene-based and therefore quite noxious; make sure you have adequate ventilation and take care when handling it. Spray around the needle/crown cap on the exterior of the ‘brush as well as inside the colour cup to remove any traces of colouring agent. I remove the needle and wipe it in a tissue soaked in the appropriate cleaning agent and re-lubricate using an airbrush oil or a very tiny quantity of Vaseline, before reassembly.

Strippers

Some modellers dismantle their airbrushes every time they use them and I agree that every so often it is a good idea to strip down the airbrush and thoroughly clean every part, but I would never recommend you strip your airbrush over the sink, as small parts have been known to disappear down the plughole! When the airbrush is in pieces, you can soak small nozzles overnight in cleaner, but never stand the whole airbrush in a pot of solvent because this will destroy the seals. If you have had a blockage in your nozzle, you can use a cocktail stick to help dislodge stubborn congealed paint (Photo 6), but don’t use wire since it may distort the aperture and damage the airbrush. When you reassemble the airbrush make sure the needle is seated fully home by rotating it, then close the needle locknut Be very careful not to damage the fine point of the needle during this process.

Priming

Many modellers choose a proprietary car

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aerosol primer and this is perfectly adequate, except that you have little control over the volume of spray. Priming can show up defects in the build, which can then be corrected before the application of the final finish. It is not strictly necessary to prime if using enamel paints, but you must use one for water-based paints because they do not adhere directly to plastics. There are now some very good primers made especially for the model market, rather than the ubiquitous Halfords primer! (Photo 7)

Mixing paints

I’m often asked about mixing paints for airbrushing and it certainly can be confusing because there is no hard and fast rule about how much thinner to use to get the right consistency. It is not a black art, however, and can be mastered as soon as you know what you are aiming for. Some air-brushing colouring agents, for example the Alclad and Vallejo Air ranges do not require mixing at all. For those types that do need thinning, the amount of thinning agent to use will depend upon the viscosity of the paint to be thinned. Not all paints of the same range will be of the same consistency when you first open the jar and of course they thicken and age at differing rates also. What you are aiming for is a liquid the consistency of milk. What does this mean? Put simply, when you have thinned the paint with an appropriate thinning agent, you should, when swirling it inside a glass jar, get a film of liquid adhering to the side of the jar which is not transparent but lets light through the colour and which does not leave spots of solid pigment (Photo 8). Gravity fed airbrushes can operate successfully with paint that is slightly thicker than those with side feed or suction cups, because the force of gravity is also engaged in pushing the paint into the nozzle and this is the reason some modellers prefer them. If you manage to over-thin your paint, it is better to throw it away rather than add more paint to rescue it, because you will use far more paint than if you were to start again. Once your paint is ready, practice again on plastic card to improve your technique and to ensure the mix is good.

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Application of primers and top coats follows the same general principle. Start in the least accessible parts of the model, inside tight corners, so that you avoid getting patches of grainy over-spray in highly visible areas and end with an evenly coated piece of work, instead of trying to paint gaps after you’ve covered the main part of the model (Photos 9 and 10).

When you run an airbrush over an area painted previously, the expelled air dries the paint applied earlier, since it creates airflow in pockets and corners. As you work larger areas, work in a methodical way, increasing the coloured area by extending it at the wet edge of the paint the whole time. It helps if you have a plan of your work and know exactly where you are going to paint next. On flat areas, where you

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change the direction of your stroke you will end with a high build up of paint, so ensure your stroke goes across and then beyond the model (or onto a masked area which is to have a different colour), in order to avoid this. If, having applied an area of colour, your work looks dry and grainy, you need to increase the amount of paint you are applying. If, in contrast, it accumulates into drips, you need to reduce the quantity you are putting on. The viscosity as well as the colour of the paint will dictate how many coats are needed for good coverage. For example, strong pigments like black may cover in one coat, but yellows or whites may look transparent after one coat and need several more for good coverage.

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