I’ve been on a quest over the last few months to find a solution to spraying very fine lines with an airbrush repeatably and reliably. Call me crazy but when I own a high end airbrush like an Iwata Custom Micron or similar, I expect them to behave like a professional instrument that works on demand when properly maintained. What I was getting was a tool that would not live up to the fine line test samples included in the box by Iwata. I’ve done several things to improve the situation. First I’ve switched over my paints from Iwata’s ComArt paint to Holbein’s Acryla Gouache in 20mL tubes. This didn’t solve the tip buildup problem, but a resulted in a much smoother and finer pigment with better coverage and opacity. My next step was the follow Kim McCann’s advice and polish the taper of my needles to a mirror finish using a jeweler’s rouge. This again improved the tip buildup problem and consistency doing fine lines - but only to a point. My next step was experimenting with certain dilutions of water with Winsor & Newton’s Acrylic Flow Improver. I found that I could achieve very fine and consistent lines using a 100% mixture of the flow improver, but it is severe price. The high concentration mixture of flow improver will inhibit the ability of the gouache to adhere and cure to the subtrate. This makes it susceptible to flaking and lifting when Frisket masks are used. Beginning to run out of options, I returned to a book in my library, The Illustrator’s Bible by Rob Howard and read the chapter on gouache again. Ox Gall has been used by watercolor artists for many years to improve flow and blending of paint and to improve drying. Howard’s book recommended the use of Ox Gall to improve the flow of gouache paint, and stated this was popular with airbrush illustrators for limiting clogging problems. Out of desperation, and a little skeptical that it would work, I ordered a 40 mL bottle of Holbein Ox Gall. When it arrived, I made a mix in a 1 ounce dropper bottle of 1 ounce of water to 15 to 20 drops of ox gall and used that for mixing with the tube gouache. I was pleasantly shocked by the results. Not only did it eliminate the inconsistency and limitations on doing fine lines, but it solved the coverage problem and fragility when placing adhesive Friskets on top of it. To test this, I used an Iwata Custom Micron CM-B with a polished needle taper. Paints are Holbein Acryla gouache on a medium press sketchbook paper. I sprayed both fine lines and a heavy area coverage. Below is a test of the gouache reduced with the water and ox gall mixture. The heavy area coverage was than covered with a piece of frisket film overnight, then the frisket was peeled off and the piece was examined. The ox gall mixture seems to have not only sprayed fine lines very well and repeatably, but gave excellent coverage in a heavy application which was resistant to adhesive backed masking film. NOTE: small white patch in lower left hand corner was a negative workability test using an electric eraser, which it passed. Next I attempted a similar test using the 100% Windsor and Newton Acrylic Flow Improver to reduce the Gouache. This flow improver mixture passed the fine line test, though not as well as the ox gall mixture did. But it then failed miserably when the frisket was applied over it and left to sit for six hours. You can see how much paint was lifted off by the adhesive on the frisket. My conclusions are that the ox gall, when mixed with water in trace amounts solved the fine line problems without affecting the ability of the paint to cure. This stuff really does work! I’ll continue to conduct tests on this. Specifically I’m curious to see how ox gall would work with Createx or ComArt paints, or used in airbrushes which do not have hand polished needles.