Types of Airbrushes
Single-Action Airbrushes vs. Double-Action Airbrushes
"Single-action" and "double-action" refers to how
the artist controls the airbrush’s air and paint flow. Single-action
means that it sprays much like an aerosol can: just push down the trigger
to get it to spray. The amount of paint that comes out is controlled
by twisting a knob or screw located near the tip. This type of airbrush
is also referred to as an "external-mix" because the air and
paint actually mix in front of the needle. There are fewer moving parts
that need to be cleaned, therefore it is an easy airbrush to maintain.
The trade-off is that one does not have the precise control offered
by a double-action. However, a single action is a great beginner’s
brush that will always have uses no matter how advanced an artist becomes.
Smooth gradations are easily accomplished, and for many artists, this
will be the only airbrush they will ever need.
For the best control, such as fine lines and the ability to produce
thick-thin strokes (the classic "dagger stroke"), a double-action
airbrush is essential. Also known as "internal-mix" airbrushes
because the air and paint mix inside the nozzle, this type of airbrush
has two trigger movements. As with the single-action, air is controlled
by pressing the trigger down.
The amount of paint spraying out is controlled by pulling back on the
trigger. The farther the trigger is pulled back, the more paint comes
out. This allows for absolute control of the paint. T-shirt lettering
is vastly easier with this type of airbrush. Experienced, "freehand"
(painting without the aid of masking materials) airbrushers can control
a double-action to produce photo-realistic artwork.
Siphon-Feed Airbrushes vs. Gravity-Feed Airbrushes
These terms refer to how the paint is supplied to an airbrush. Although
this feature does not directly influence how an airbrush performs, it
does indicate the paint capacity allowed before refilling.
Siphon-feed means that the color-cup attaches from underneath the body
of the airbrush. Air suction pulls the paint from the cup to the nozzle
area, where it comes in contact with the air. This type is useful when
spraying for extended periods of time because the color-cup (typically
1/2 ounce capacity) can be taken off and a bottle can be attached, normally
with a capacity of 3 fluid ounces or less.
Gravity-feed essentially means that the color-cup is on top of the
airbrush body. Most models have an immovable color-cup. Although larger
models can have paint reservoirs of 2 ounces, gravity feed airbrushes
are made for detail, where small amounts of paint are applied at one
time. Because the paint is in an open color-cup, some models offer a
separate cap to keep paint from drying out in the color-cup. They have
a tiny hole in the center of the cap to prevent a vacuum from developing.
It is essential that this hole be open to maintain proper paint flow.
Siphon-feed bottles also have this hole on the cap for the same purpose.
Needles and Nozzles
The Airbrush Needle and Nozzle
All airbrushes work on the same principle; air and paint meet at an
exact point in space. At that point in space there is a tapered "needle"
that projects the combined air and paint forward. This simple concept
was used by Neolithic man on the walls of his cave. He would orally
grind up the "pigments", anything from charcoal to berry juice,
in his mouth, with saliva being the "binder". His lungs were
the air source, his mouth was the nozzle and his tongue was the needle.
Fortunately, the airbrush was invented around the turn of this century,
making the modern airbrusher’s life much easier.
Obviously, a human tongue is a very blunt, tapered needle that will
not allow an artist to spray fine lines. Fine line spraying requires
very delicate needles tapered to a delicate point. Large commercial
spray guns, such as those used for automotive painting, have blunt needles
that do not have much of a taper. However, their shape is made to fit
into a large nozzle that can deliver great amounts of paint. The finest
detail airbrushes have a nozzle size of .18mm.
The "nozzle" is the part of the airbrush head assembly in
which the needle rests. It is tapered exactly the same as the needle
it holds. On a single-action airbrush, when the screw is twisted, it
widens the space between the needle and nozzle by moving the nozzle.
In a double-action airbrush, when the trigger is pulled back, it moves
the needle back as well. The farther back the needle moves, the larger
the space between the needle and nozzle.
Controlling Atomization
What is "Atomization" ?
Atomization refers to how fine the particles being sprayed are being
broken apart. In a garden hose, when there is a light mist of water
sprayed, the nozzle is finely atomizing the water. Higher water pressure
will allow for finer atomization. In an airbrush, instead of water pressure
dictating the atomization, it is accomplished with air. Airbrush nozzle
head assemblies have amazing baffling systems that funnel the air around
the needle so that the air can atomize the paint evenly. This action
gives the airbrush precision.
The better the atomization the smaller the drops of paint and the closer
together they are. This provides a more solid coverage and finer lines.
Atomization in airbrushes is the same as DPI (dots per inch) in computer
printers. The more dots per inch the higher the resolution, which results
in better output. In airbrushes the higher the atomization the crisper
the image. Atomization will be rated on a 1-10 scale (1 being poor and
10 high) for a better idea of the spray quality of the brush.
Atomization is Controlled by Air Pressure, Air Baffling and Paint
Thickness
While there is nothing that one can do to alter the baffling of a given
airbrush, the air pressure and paint thickness, or "viscosity",
can be adjusted to suit a particular need.
Air pressure is measured in pounds per square inch, commonly referred
to as "P.S.I.". As mentioned above, pressure influences atomization.
In an airbrush equipped with a fine needle, less pressure is required
to produce good atomization. This important aspect needs to be addressed
before one can decide what the proper paint viscosity is.
Not enough pressure results in a stipple paint effect, too much pressure
causes "overspray", a soft halo of color surrounding the area
intended to be sprayed.
Paint Thickness Differences
The viscosity of the paint to be sprayed is also equally important.
Viscosity is measured in Centipoise (cPs). 1 Centipoise is the resistance
of water, hence water has a viscosity of 1 cPs. Golden’s ready
to spray Airbrush Colors have a viscosity range of 40 - 60 cPs, making
them ideal for illustration and fine art. Most textile airbrush colors
range from 100 to 400 cPs. A typical house paint is 3000 - 6000 cPs.
If the airbrush is set to an adequate pressure and spattering still
occurs, the paint is too thick to be properly atomized. Sometimes raising
the P.S.I. can eliminate the spattering, but the correct procedure is
to thin the paint. Over thinning can also have adverse effects, therefore
switching to a larger needle/nozzle airbrush is also an option the artist
must consider.
Matching
an Airbrush to the Proper Pressure & Paint System
By understanding all of the above information,
an artist can choose the type of airbrush needed for each specific task.
For example, when excellent atomization and precision spraying is required
(such as with commercial illustration), an airbrush needs to have a
fine needle that will work with low pressure (15 - 40 P.S.I.) and low-viscosity
paints.
Conversely, t-shirt artists prefer a thicker paint because it will have
less overspray. They tend to spray at 60 - 100 P.S.I. and require an
airbrush that will accommodate the higher pressure and thicker paint.
To properly spray housepaint, the spray equipment has a large nozzle
and a different baffling system that will allow it to spray at 40 -
60 P.S.I. but atomize like it was at a higher pressure.
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