Iacopo, did you never seriously get into the laser balancing method with the reflection from the flywheel (Quark top style)? Especially with your shiny flywheels that you make? You would only have to make sure a few millimeters on the upper side are flat. Also with your lathe you could check some things while the top is still on the lathe.
Yes, I did, it was Alan Adler who explained me how to do it exactly. I built my top Nr. 22 for to be balanced in that way, with a flat, mirror polished area on top of the flywheel. The method works, but I preferred the paint and brush, so I didn't make any other tops in that way, (even if the upper parts of my flywheels are polished, they are not flat, but rounded, and they cannot be used with that technique). I don't like to copy the ideas of the others, when they are so particular and characteristic. Also I was used to the paint and brush which work very well for me, and I didn't really feel the necessity to make things otherwise.
Instead of brush and paint I tried a black marker on my brass flywheel. I rubbed the marks away with alcohol. Over all I did not find it very useful for in my case.
Maybe one reason that the brush and paint work well for me is that my tops, having spiked tips and tiny bases, are steady, do not walk on the spinning surface while spinning, and this makes this technique easier. Also, by the time, I improved the technique: for example, I cut nearly all the bristles away from my brush, leaving only three of them in place. The amount of paint on the bristles and the amount of the water in the paint are important too. The aim is to try not to deviate the movement of the top while the brush is in contact with the stem, or the mark position will be less accurate.
The disk has sectors of different colours, say red, yellow, green and blue.
When I started making tops, I was unable to balance them, and I was so angry about it that I made a big effort to solve the problem, I really wanted a very good balance in my tops.
In the end I found how to do it and even made two videos about how to balance tops.
I also tried with the coloured sectors, in various ways, long time ago.
I tried the disk with the colours like in the Maxwell top.
I tried to paint the stem with vertical strips of different colours, then a grazing light illuminating a tiny side of the stem when the stem was tilted towards it, made evident the direction of the leaning.
I still have the painted sectors in one of my old tops, for one of those my experiments.
But all these techniques with the coloured sectors were not accurate, relatively to the paint and brush technique, so I stopped experimenting with them.