This technique will require practice. The objective is for a smooth non-lined appearance. Removing mat for texture and shading appearances use your scrubs. Experimentation of the different brushes gathered, would be the only source of finding the brushes that are right in this application. The brushes need to be firm.
Different sizes are necessary.
Cutting the bristle and sealing with a flame can change the sizes. I strongly recommend experimenting. It is the only source for finding the right brushes for the job. Fire the project in the kiln, according to temperature recommendations for the stain. Typically fire to 1300F. Adding color from the enamels is the last step.