October 31, 2012

Pigment particle size in airbrush paint

Up to a few days ago, I used to think that airbrush paints could roughly be divided in two categories that determined the ease with which they could be sprayed:
  1. Paint consisting of coarse pigment particles
  2. Paint consisting of fine pigment particles
After reading two rather deep digging articles about the measuring of particle size and their behavior, I began to realize that matters may be slightly more complex than I had been thinking before reading those. The articles dealing with these matters have unfortunately been removed from the web.

Paint pigments

It appears that measuring particle size is quite unlike what I imagined to be. I believed it was similar to measuring the difference in size of a soccer ball or ball bearing on a much smaller scale. Those are nicely spherical objects that have a tolerable deviation from the perfect geometric shape. Pigment particles in paint however, have rather wayward shapes that aren't detectable by the naked eye, but they can be made visible by using a microscope. Some substances like TiO2 (titanium oxyde - present in a number of white paints) are said not to be measurable at all... I assume that is caused by their reluctance to dissolve in an orderly fashion inside a solution.

An other remark in the articles that struck me, is that particles that are relatively large, but have a shape loosely approaching a sphere will be processed easier than smaller particles that have a more irregular shape. So my dislike of Createx paints could have different reasons than I previously believed, Createx being sort of a pain to spray compared to paints like Lukas Illu-Color, Inspire H2O and Holbein Aeroflash for instance.

Also the properties of various types of liquids in which the particles are dispersed, determine the paint's behavior in an airbrush to make the complexity of this matter worse. Bear in mind the excellent behavior of solvent based paints versus the comparatively mediocre handling of most waterborne paints. The crux of the matter is that the pigments in both solvent based and water based paints are the same.... Everyone buys from the same suppliers that do not give exclusive rights to any client because they just want to sell as much as possible. So, the pigment particle size is NOT the determining factor in the quality of handling of a type of paint. The clusters formed by the particles inside the solvent fluid cause paint to be sprayed easily or with difficulty. This means that the quality of the solvents make a paint behave well or badly.

I could probably add to this, that the gas with which paint is propelled out of an airbrush gun could affect the process of spraying too. I recall spraying with CO2 once, because I was told that it does not contain any mixture disrupting, unwanted moisture from condensation in the compressor. I was unable to detect a significant difference. Probably because the moisture trap fitted to the compressor or between the air hose and the airbrush removes any unwanted fumes before they have a chance to clutter up the paint, but something else came to mind here, now that I became aware that there seems to be no end to the complexity of matters that are commonly believed to be dead simple.

The idea behind using CO2 instead of air would be that paints are designed to dry when they are in contact with air. So if you airbrush with air, that drying process may theoretically start sooner than when using CO2 as a propellant. A few nano seconds in the process of drying could probably be enough to make the difference between spraying good and not so good, because that is the time it takes for the paint droplets to travel from the airbrush to the surface an artist is spraying on. Assuming of course that paint does not dry as quick when exposed to CO2 than it would when coming in contact with air. But, as I said above, there wasn't a noticeable gain in using CO2 in my experience.

All this confusion made me reconsider the possibility of spraying with the type of paint that actually isn't a paint: watercolor dyes. These type of liquids were involved in my first encounters with the art of airbrushing. These attempts to produce something that would not injure the eyeballs were probably as disastrous as anyone else's, but these dyes hardly gave any tip dry at all and they seemed to remain wet a lot longer than the waterborne acrylics that are commonly used by the airbrushing trade (if my memory serves me right).

Later however, I gradually learned to appreciate the behavior of inks in an airbrush a lot. If artists are not comfortable with spraying transparent, low viscosity mediums while using ultra low air pressures (less than 10 psi or so - I hardly ever peek at the pressure gauge), then they will probably not consider spraying watercolor dyes to be an appealing option. But I am going to try it anyway because of my cherished experience with inks and because of the muddiness caused by the articles that I referred to.

The color range in which inks are available is a lot narrower than that of waterborne acrylic paints, but versatile enough to give it a try. The ink that I used to spray with decades ago, with all sorts or delight - Rotring Artist Color - is no longer in production (probably because it was terminated by some brain dead manager, whose closest encounter with art was when he was forced to finger paint in kindergarten).

Here I found a site that sells inks made by a company which name faintly rings a bell in the back of my mind. And here is an other one that I may visit to obtain inks to test. If I have any luck with that you will find the results somewhere in this blog later, if not I may still put the failure up for fellow artists to benefit from the experience of my mess up and continue to struggle with whatever blubber clogs up my airbrush less than other brands of blubber while allowing me to spray finer lines. But to be honest, I don't expect the ink situation to be any better than or different from the confusing realm of paint, but I will try a number of options and record my findings in this blog some time.

Corporate espionage

A few worth knowing notes, vaguely related to the above: Some ten years ago I was involved in the development of a new type of paint. What distinguished it from the solvent based paints, was that is was based on alcohol (and therefore more or less organic and bio-degradable while not as hazardous as solvent based paints) and excellently suited to use as a strong temporary paint that was easily removable with an alcohol solution without leaving any trace on the underlying surface or causing damage to the environment. So I know a thing or two about paint. But with an emphasis on the artistic and commercial use, I must admit.

When discussing the paint's composition with the university of Groningen (The Netherlands) lab we were collaborating with, they told me that on average a paint contains around 50 (!) masking substances meant to confuse the competition that was always trying to analyze the paints of  'the enemy' and steal ideas to improve their own products or produce new types of paint. It also became clear to me in that conversation that no infallible guarantees could be given that those substances had no effect at all on the behavior of the paint, but that it was necessary to stay in business nevertheless.... I assume that between the period of that talk and the present little has changed in the shadowy department of paint development.

An other weird accident that I would like to mention here, is an encounter I once had during an airbrush fair with a well known artist (whose name I will not reveal). He was hired by a paint company to give demonstrations and made beautiful art. But when we got to know each other better while hanging out in our booths and that of fellow artists, he confided to me that the paint he was supposed to work with sucked, but the company paid well. So he threw away that manufacturer's paint and refilled the bottles with his own favorite brand... No one noticed anyway and his reputation as a skilled artist would remain in tact, while the company that he worked for would be considered to produce excellent paints in the perception of unaware clients....

This kind of practice I suspect to be more common than is commonly believed. So, don't trust advertisements, demonstrations or any unsubstantiated hear say, just do your own testing and experimenting. Or visit this blog to learn of course...., because I have no obligation towards any paint producing corporation whatsoever - no contracts, no buddies who work there or outlandishly beautiful secretary (unfortunately) that seduced me into sharing profit boosting rubbish etc.