This time I thought I'd describe the brushes I use and how I maintain and use them.
Below is a picture of the brushes I use. I don't have a whole quill full, just these five (that I use regularly). I do have some backups in a package, but I've been using these for over 10 years, and they serve well. It is important to note that you don't need to get the best, most expensive sable brushes that money can buy. These were bought off the rack at a Hobbytown USA store for a pittance. The big difference is maintaining the brushes so they keep their original shape and softness.
From left to right, the brushes are 1) about a size 6 flat brush used for painting glue on masonite stands, and putting down the pigment after the glue and sand dry. It is also used for drybrushing the lighter sand colors on the bases after the earth color is laid down. The second brush (2) is a size zero brush with the point judiciously cut off it with really sharp scissors. This is for painting large areas on horse figures, and touching up bases after the glue and first layer of pigment dries. The third brush (3) is for finely localized dry brushing techniques - specifically the musculature of AB horses. It is another cropped size zero brush, but shorter so that it acts as a miniature shaving brush. It's singularly effective for that purpose. The brushes I use on the actual figures are brushes 4 & 5. These are kept to a very fine point so that fine detail can be achieved. The larger brush (4) is a double-zero size, and the smaller brush (5) is a 10/0 brush. The important thing is to keep the points very sharp on these brushes.
The next picture shows the 00 and 10/0 brush next to an unprimed and unpainted AB figure, so you can see the relative size of the brushes and the 15mm figure. In this picture, you should be able to clearly see the advantage of keeping the brushes clear and pointed, especially when doing very fine work like collar piping, faces, etc.
To maintain the brushes, I always wash them with soap and water after a painting session. After rinsing the soap out of the brush, I twist the point so that it stays good and sharp for the next painting session. Simply doing that has allowed me to use these relatively cheap (inexpensive) brushes for over a decade.
That's most of the secret to making highly detailed Napoleonic figures. The other issues are a) have good optics. I use the Opti-Visor #5 (available at most hobby stores). The advantage there is that you see in macro (like the photo above), but with binocular vision. This means that you can see depth as well as detail - you always know exactly where the brush is on the figure, and how the paint attaches. The last ingredient is a sense of color, which I'll post about later.