A Reprint of an Article in The Coupling of September 1996 - by Ken Sherwood

Airbrushes

There are two main types of air brush: single action and double action.

In a single action airbrush the trigger is used only to control the supply of air to the spray head, the paint flow being preset by moving the needle via an adjusting screw forward for fine spray, and back for wider spray. Dual action airbrushes use the trigger to adjust both air and paint supply to the tip. Pushing the trigger down adjusts air supply/pressure and pulling the trigger back releases the paint supply. The further the trigger is pulled back, the larger the volume of paint is sprayed. Proper triggering of the air brush is down for air, and back for paint flow.

In general, the single action airbrush is easier to use for the beginner than the double action one. However, once the dual control of the latter is mastered, the versatility and spray effects achievable realize the full potential of an airbrush. The dual action brush is the choice of most professional airbrush artists.

Air Supply

Most hobbyists use a small bleeder type of air compressor. These can be used connected directly to the airbrush, although some modellers prefer to use it connected to and air tank and use this to control the pressure to the brush. Unless you are airbrushing large areas or airbrushing professionally, this set up is more of a 'want' than a 'need'.

However, the use of a watertrap between the compressor and air brush, especially in the humid air of summer and damp basements is very definitely a 'need'; there is nothing more frustrating than having a good paint job suddenly ruined by small droplets of water on the surface of the model.

Other sources of air are:

1. Compressed air tank with pressure gauge and regulator (scuba tank) refilled as required.
2. A large inner tube filed with air!
3. 'Propel' pressure canisters. These are not recommended as they have a propensity to ice up and loose pressure very quickly, as well as initially being at too high a pressure. With their cost it is better to save up for a portable compressor.
4. Carbon Dioxide carbonation (fizzy drinks!) cylinders.

Technique

Best paint results are achieved by using a constant motion parallel to, and across, the surface to be painted, at a distance of about 6 inches. There is a tendency for beginners to spray with an arcing motion which will result in an uneven paint finish and paint build-up. The spray should be started just before the surface to be painted and carry through beyond the end of it. With practice only slightly wet paint will reach the surface of the model which is ideal for most flat finishes. For gloss finishes the paint should look wet on the model surface to allow it to flow out as if brushed. This may require more solvent or moving the airbrush closer to the model. The airbrush adjustments allow you to control the amount of paint and air such that you can spray from 1/16th line up to a 1 1/2" band with the medium tip installed.

Head Assemblies (Badger Nomenclature)

• XF Fine detailing head will spray from size of a period up to approximately one inch.
• IL Will spray a line about one sixteenth up to one and half inches.
• HD Will spray from about one eighth to two + inches, uses some four times the amount of paint than that of the fine tip.

Troubleshooting

Paint Runs and Blobs

Spraying too close to the surface and/or not moving the brush beyond the work before shutting off the paint. Paint thinned too much.

1. Move airbrush further away from model.
2. Decrease supply of paint.
3. Decrease air pressure.
4. Thicken paint.

Centipedes

Caused by spraying too close to subject. Paint too thin.

1. Move airbrush away from model.
2. Thicken paint.

Rough and Grainy Surface

Paint too thick, or not enough air pressure. Airbrush too far away from work.

1. Move airbrush closer.
2. Increase thinner in paint.
3. Increase air pressure.

Maintenance

Cleanliness is very important in the performance of an airbrush. The small passages inside the brush can quickly become blocked with dry paint, especially so when using the enamels. Thus it is always advisable to spray solvent through the air brush after each use. For acrylics and enamels, spraying acetone is quick and efficient; alternatively, use Isopropanol for acrylics and Varsol for enamels. After spray cleaning, carefully remove the needle and wipe clean. Clean spraying tip and paint cup with a fine brush or with small pieces of rolled up paper towel soaked in solvent.

WARNING

All solvents mentioned are toxic to a greater or lesser degree and are also inflammable. ALWAYS use in a well ventilated area away from naked flames and wear a dust mask. DO NOT SMOKE

Spraying Enamels

Humbrol and ModelMaster

In general these paints require thinning in a 1:2 paint to solvent ratio, using proprietary solvents or Varsol. Humbrol can diluted with xylene which evaporates much more quickly resulting in improved spraying and giving a smoother finish. However, XYLENE IS VERY TOXIC, and should only be used in well ventilated areas. USE A BREATHING MASK.

Humbrol paints in general have excellent covering power, but the pigments used are relatively coarse and will tend to hide any fine detail. However this can be a plus in that the paint will flow and cover minor imperfections. They also vary in viscosity from tin to tin and may therefore require more thinning than the 1:2 recommended.

Floquil Paints

These can usually be sprayed out of the bottle but if thinning is required, use a 3:1 ratio. These paints do give excellent covering without hiding detail. The older paints had as a solvent Diosol, which was a mixture of ethyl benzene, toluene and xylene, which was extremely toxic and flammable. More recently they have converted to a solvent based on petroleum distillates. c.f. Varsol which is somewhat less harmful.

Acrylics

Acrylics are safer to use than comparable solvent based systems (which often contain toluene). That said, while being less toxic, they nevertheless do contain alcohols and a sensible precaution is to always wear a spray (dust) mask. Further, the pigments in acrylics are even more finely ground than those in enamels and are easier to inhale. So if you do not have a spray booth always ensure that the area is well ventilated and that there are no naked flames about.

While many manufacturers recommend diluting with 10% distilled water for spraying, thinning with pure Isopropanol (IPA) gives a superior spraying capability as it reduces the surface tension of the water in the paint, allowing it to cover more evenly, and is sufficiently volatile to be almost evaporated before hitting the model surface. The thinning ratio will vary from manufacturer to manufacturer but both Tamiya and Gunze paints are thinned in a 1:1 ratio for best results.

Acrylics are very unforgiving as spray paints in that every minor imperfection will show in the finished model. cf. enamels. However, the bonus is that no detail is covered. They are particularly sensitive to oily surfaces such a mold release agents, finger prints and solvents. This means that you must clean any model with a solution of dishwashing liquid by scrubbing with an old toothbrush, otherwise the acrylics will in all probability not adhere very well to the substrate. Even though they are touch dry very rapidly, models are best not handled for at least 24 hours, and even then it is best to handle wearing a disposable latex glove to avoid any finger prints on the finish. Generally, after 72 hours models can be handled without gloves. Leaching from enamels can cause discolouration in some of the lighter colours when being oversprayed. Because of their fast drying time most acrylics do not hand brush particularly well.

Masking of acrylics can usually be done after 48 to 72 hours, using any of the semi tacky masking tapes such as 'Kleen Edge' or artists 'Foto Frisket' films. Using standard masking tapes is not recommended as they will invariably lift some of the paint and they do not usually give a very clean edge. The use of latex (maskol) will not affect the paint surface.

Some decal setting solutions such as Solvaset, will lift the paint film if sufficient drying time has not been allowed. A simple measuring device for paint and thinners is an eye dropper suitable marked at intervals with thin strips of masking tape wrapped around.

Pure Isopropanol (IPA) can be obtained from most drug stores directly from the pharmacist. DO NOT USE RUBBING ALCOHOL, although this is around 95% IPA, it does contain water and sometimes small amounts of oils.

Common Manufacturers

Gunze Sangyo

A wide range of colours produced many to FS595 and BS 381C Specifications. There are both flat and gloss colours, the former producing a semi-gloss sheen which takes decals very well. There are 73 general colours including metallics, weathering and fluorescents. Also there are 73 military colours, many made to the above standard specifications.

Floquil Polly-S

Covers basically many of the Floquil solvent based colours. There are 51 railroad colours as well as 6 weathering and 31 general colours. Unlike many of the acrylics these can be hand brushed with a small amount of thinner added. Thinning ratio recommended is 3:2.

Tamiya

There are 67 general colours, some of which match Federal standards. They are not easily hand brushed. Thinning ratio is usually 1:1.

Testor Model Master

There are 60 colours, many of which are matched to FS595, and 10 are match to standard NA auto colours

Your author is not aware of any UK acrylic paints matched to pre-grouping or BR standards. If anyone has any information on such materials, please share it with us.

© Ken Sherwood - 1996

Back to our main page