I used to make candles. I still do occasionally when I have a load of stumps lying around.

Most bullauns are hemi-spherical. A few are flat bottomed. Some are rough. In County Carlow they are cone shaped and huge (very trendy candles?) [Carlow is odd because this is also where you find all the grooved stones like the Devils's Arrows. Carlow also has the only rock art spirals on a horizontal panel - Stan once said there were none, don't know if he's changed his mind since then though]

At 40cms across many bullauns are just too big for candles, but the ones in or around crosses are often small. Perhaps a floating wick in oil?

I will not discount any purpose, but I do have my favourite theories. I believe I can also push back the <i>establishment's</i> accepted earliest date by a very long time indeed.

For the rest you'll have to buy the book ... which isn't written yet :-)