Titanium and Steel balls sounded a bit too 'zingy'. The ceramics sounded superior to me.
There are three hi-tech ceramics that were used : Alumina, Silicon Nitride and Zirconia. The Silicon Nitride balls are surprisingly light, whereas the Zirconia balls are around twice as heavy. Alumina sits in the middle for density. All are very hard, harder than tool steels and titanium.
Initially I used 18mm balls, the same size as the lead balls that I found worked best. Alumina gave the best results at this size. So we tried other sizes, down to 10mm. Turns out that the 12mm balls gave the most balanced sound.
So I was just about to go into production with 12mm Alumina balls when I discovered that using one Zirconia ball and two Alumina gave a distinct boost in performance. This came about because Richard, (who runs Krebs Upgrades), showed me the same soft of effect on his footers. He says it's down to there being a preferential path to ground and faster transmission speed. That sounds plausible but it's still surprising that it's such a large effect.
So I decided to go with the mixture of Alumina and Zirconia ceramic balls.
How They Sound
Compared to regular Blackpods, they seem 'faster' and convey a little more information, especially at the top end (treble). But at the same time they are relaxed and musical.
The extra jump in performance that you get with the Z-ball/2xAlumina is larger than any difference between ball materials.
How to Use
To get the best results from Ceramic BlackPods, you should be prepared to do a little experimenting. On some components you get best results with the balls pointing up, while on others you need the ball downwards. Also there are the locations to trial - the sound can vary considerably with different positioning. Also be sure that the flat side of the Blackpods makes good contact - don't put it against a bolt for instance - it should be flush with the component or base.
Finally there is the position of the Z-ball. The Zirconia ball is marked with a Z sticker, but it's quite easy to see the color difference in daylight - Alumina is slightly ivory-colored, with Zirconia blue-white.
I usually start with the Z-ball carrying the most weight - normally with components you find that the weight in unevenly distributed and this results in each Blackpod taking a different load.
You may even find that you get the best performance with one of the Blackpods upside down compared to the others. Just don't despair if they don't sound great to start with - try turning them over..