That's a very common and popular technique in ceramics to make multicolored patterns and designs. Variations on that process make a bunch of different fancy porcelains and ceramics. I haven't ever seen enamel dials done that way though. If they were porcelain it would be perfectly sensible. But it's my understanding that enamel for dials starts out as a crushed powder of glass which is melted and fused. I just don't imagine a practical way to control the details using that process. It's possible, but I think not practical. I am very curious now though. Look forward to hearing from Jon about it.