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Arron
20th August 2016, 04:59 PM
Do we have someone experienced with airbrushes on the forum who could answer a couple of questions? The questions relate to doing fine detail work with airbrushes.

Cheers
Arron

Cliff Rogers
20th August 2016, 09:56 PM
35 years ago, fire away.

Arron
21st August 2016, 11:49 AM
Thanks Cliff
here goes

My problem is the airbrushes start with a good paint flow but the paint flow peters out to nil after a few seconds. This happens only when doing detail
work (say lines under 2 or 3mm wide), when I'm doing thicker stuff its no problem (not surprising, there being a much greater air and paint flow). It
only occurs with certain paints (more below).

The problem is not 'tip dry', the tip is still moist and the paint will flow if I stop and restart (although it promptly peters out again).

This is the setup.
2.5 hp compressor. Regulator and 2 water filters fitted.
One Iwata HP-CS airbrush with 0.3mm.
One Generic airbrush with 0.2mm.
Both airbrushes are gravity feed with 15ml cups.

Using acrylic paints.

I've tried every possible viscosity from thick to like water.
I've tried every possible pressure from 6 psi to 40 psi.
I've tried every possible different combination of these two.

I've tried retarder and liquifying medium.

The paints which work and dont cause this problem are:
1. cheapo airbrush paints from Aldi
2. Tamiya acrylic.

The paints which do experience the problem are:
1. Golden High Flow Acrylic
2. Matisse Flow Acrylic

Both the latter two are rated for airbrush use. In fact the Golden is apparently just their old airbrush paint renamed. The Matisse is not quite the
quality of the golden products, but is claimed to be very fine pigments and suitable for airbrush with sub 0.1mm nozzle (if you could find such a thing).

So my question is why does this happen with two paints and not the other two, when all are airbrush-rated and all are tested with identical properties
of viscosity, additives, pressure etc. There must be something else I cant see and cant measure. I thought of surface tension but that should
work in the opposite way - be hard to break but then flow more easily, not stop flowing.

FYI, in case you are wondering why it is important to get the Golden and Matisse products to work, its because they are easily available to me
and come in the old familiar artist colours like burnt umber and raw sienna, not 'Nato Green' and 'Desert Brown'. Also, most of the airbrush
paint colours are lurid, while I am wanting a wide range of earth colours and subtle shades of grey (without mixing my own, due to issues of cost and repeatability).

Alternatively, if anyone knows a good active art or airbrush forum (ie one like wwf) where I could ask this, please let me know.

tia
Arron

Cliff Rogers
21st August 2016, 09:59 PM
Wow, that is weird.

As you have already worked out it must be something to do with the physical properties of the paint, see the stuff I quoted from Wiki below.

I have not struck the problem but then I haven't done anything that fine either & I've only ever used Automotive Acrylic, like you said, lurid colours.

There is an Airbrush forum but I haven't been there to know how active it is. Airbrush Forum (http://www.airbrushforum.org/)

I'd like to try ink & water colour on timber for decorating musical instruments but I have FAR too many projects on the go.

Best of luck with that.


Properties of acrylics
Grades

Commercial acrylic paints come in two grades:

Artist acrylics (professional acrylics) are created and designed to resist chemical reactions from exposure to water, ultraviolet light, and oxygen. Professional-grade acrylics have the most pigment, which allows for more medium manipulation and limits the color shift when mixed with other colors or after drying.
Student acrylics have working characteristics similar to artist acrylics, but with lower pigment concentrations, less-expensive formulas, and fewer available colors. More expensive pigments are generally replicated by hues. Colors are designed to be mixed even though color strength is lower. Hues may not have exactly the same mixing characteristics as full-strength colors.

Varieties

Heavy body acrylics are typically found in the Artist and Student Grade paints. "Heavy Body" refers to the viscosity or thickness of the paint. They are the best choice for impasto or heavier paint applications and will hold a brush or knife stroke and even a medium stiff peak. Gel Mediums ("pigment-less paints") are also available in various viscosities and used to thicken or thin paints, as well as extend paints and add transparency.

Examples of Heavy Body Acrylics are Matisse Structure Acrylic Colors, Lukas Pastos Acrylics, Liquitex Heavy Body Acrylics and Golden Heavy Body Acrylics.

Medium viscosity acrylics – Fluid acrylics, Soft body acrylics, or High Flow acrylics – have a lower viscosity but generally the same pigmentation as the Heavy Body acrylics. Available in either Artist quality or Craft quality, the cost and quality varies accordingly. These paints are good for watercolor techniques, airbrush application, or when smooth coverage is desired. Fluid acrylics can be mixed with any medium to thicken them for impasto work, or to thin them for glazing applications.

Examples of fluid acrylics include Lukascryl Liquid, Lukascryl Studio Liquitex Soft Body and Golden Fluid acrylics.

Open acrylics were created to address the one major difference between oil and acrylic paints: the shortened time it takes acrylic paints to dry. Designed by Golden Artist Colors, Inc. with a hydrophilic acrylic resin, these paints can take anywhere from a few hours to a few days, or even weeks, to dry completely, depending on paint thickness, support characteristics, temperature, and humidity.
Iridescent, pearl and interference acrylic colors combine conventional pigments with powdered mica (aluminium silicate) or powdered bronze to achieve complex visual effects. Colors have shimmering or reflective characteristics, depending on the coarseness or fineness of the powder. Iridescent colors are used in fine arts and crafts.
Acrylic gouache is like traditional gouache because it dries to a matte, opaque finish. However, unlike traditional gouache, the acrylic binder makes it water-resistant once it dries. Like craft paint, it will adhere to a variety of surfaces, not only canvas and paper. This paint is typically used by watercolorists, cartoonists, or illustrators, and for decorative or folk art applications.

Examples of acrylic gouache are Lascaux Gouache and Turner Acryl Gouache.

Craft acrylics can be used on surfaces besides canvas, such as wood, metal, fabrics, and ceramics. They are used in decorative painting techniques and faux finishes to decorate objects of ordinary life. Although colors can be mixed, pigments are often not specified. Each color line is formulated instead to achieve a wide range of premixed colors. Craft paints usually employ vinyl or PVA resins to increase adhesion and lower cost.
Interactive acrylics are all-purpose acrylic artists' colors which have the characteristic fast-drying nature of artists' acrylics, but are formulated to allow artists to delay drying when they need more working time, or re-wet their work when they want to do more wet blending.
Exterior acrylics are paints that can withstand outdoor conditions. Like craft acrylics, they adhere to many surfaces. They are more resistant to both water and ultraviolet light. This makes them the acrylic of choice for architectural murals, outdoor signs, and many faux-finishing techniques.

Arron
21st August 2016, 10:29 PM
Thanks Cliff. I've just joined that forum you recommended.
Don't know how I didn't find it myself, but it's a good one.
Cheers
Arron

Jim Carroll
22nd August 2016, 07:50 PM
Where is your pressure regulator.

It should be connected to the gun so you can have full air pressure up to the gun then regulated there so you know for sure you are getting the pressure you want .

By having only at the compressor you can have a lower pressure at the gun than is really required and the viscosity of the paint you are using is not able to flow as required

Arron
22nd August 2016, 07:57 PM
One regulator on the tank, one near the gun.

Cheers
Arron

Arron
22nd August 2016, 09:52 PM
I looked at this a bit more tonight. Ferreting around on the Matisse website, I can see I was wrong - there arent any assurances that it can be sprayed neat, rather that it should be cut with Surface Tension Medium. Apparently this is to act as a dispersant - to stop the little pigment granules clumping. So I guess that's what was happening. I didnt have any of their medium so tried dishwashing liquid, thinking that should be a pretty good dispersant. In fact it made the problem worse. So I tried Windex, which worked perfectly. Its probably no good for the long-term soundness of the paint, but this was only an experiment till I can buy some of that makers medium.

Oddly, the same trick didnt work with the Golden paints. Cutting with an alcohol-based thinner did work, but you end up with a pretty weird concotion that I wouldnt want to rely on. Anyway the golden paints are too expensive for me at $10 per 30ml.

I must say the chemistry that goes into these airbrush paints is crazy. I think you basically just have to find a maker you like and use all their products as a turnkey solution - and theirs only. No mixing, matching or homemade substitutes.

cheers
Arron