Watercolorist and inventor Charles Burdick, of Madison, Wisconsin, filed for his first(?) "paint distributer" patent on November 15, 1889. It was issued on August 12, 1890 and was for an external mix airbrush. It's basically a ruling pen  attached  to a  cup that sits in front of an air blast nozzle and when the trigger is pressed, the paint is "carried forward in a fine spray." The trigger can also be pushed forward or back to vary the space in the nib thereby controlling the width and density of the spray. Like Walkup's it is still an external mix that is similar to dipping a quill into an inkwell and blowing the ink off with a straw. While it's still a double action, thumb operated brush, it does establish two important design elements. The paint is blown forward instead of down as is done on the Walkup and it has a smaller symmetrical (hexagonal) cross section relative to Walkup's bulky rectangular one.

      In 1891, Burdick invents a revolutionary new type of "paint distributer." and he files a patent for it on January 19, 1892. The patent is granted on May 3, 1892 and is for an "air brush." It's the first U.S. patent that I've found for an internal mix airbrush or one that uses the term "air brush." Internal mix simply means that the paint and air are mixed inside the airbrush. It's very close in design to current airbrushes in that it is a double action, internal mix layout that uses Bernoulli's Principle to flow air over the tip creating a vacuum thereby drawing the paint out of the body, into the airflow and onto the object being painted.  .   Two other important features; it puts the index finger on the trigger as opposed to the thumb, and the air supply now enters from the bottom, improving the balance, control, and "feel" of the airbrush. Operation is the same as modern ones; depress the trigger for air and pull it back for paint. Another unique feature is that the paint is held inside the rear of the body somewhat like a fountain pen, hence Burdick's name "fountain air brush." When the trigger is pulled back a plug on the rear end of the needle opens a hole in the fountain and the paint flows into the forward cavity and up to the tip. It's not perfect but is better than the previous designs. The weak parts of this design are that the tip is an integral part of the body, and it uses a small rubber tube that is squeezed to control the air instead of true valve. The rear of the handle is flared, forming a base allowing it to stand it upright and, given all the paint inside, that seems like a very good idea. It was still a crude machine with way too many parts. One part it didn't have was a separate tip. This shortcoming and the overall improvement to a usable design was solved by Olaus C. Wold, the man that really made the airbrush what it is today. All of Burdick's early designs just aren't practical. How would you like an airbrush with the paint in the handle? No quick paint change here. The "fountain" feature wasn't produced. Thayer & Chandler used the term "fountain" but I have yet to see one that utilizes the feature.

      Burdick moves to England in 1893 and is granted the British patent rights to the airbrush that he has re-christened the "Aerograph." He forms the "Fountain Brush Company" in London to make clock parts and his newly patented Aerograph. In 1900 he changes the name of the company to the "Aerograph Company, Ltd." to better reflect his airbrush, the Aerograph. Burdick prospers in England.