Thank you deb for the advice. Yesterday I did the test, made a marble trying to reproduce one I made few days ago, but this time cooking very gently the fume and this is the result. At the top two pics of the marble cooked, on the bottom two pics without.
The marble cooked looks more clean and has no bubbles, what you can see is dust ( I dont know why but have a strong hability to retain estatic electricity and catch all the dust in the room
) . Another cool thing is the dots came out more shinny and with better definition. In the opposite side the another marble ( at the bottom ) has a very tiny bubbles in the edge of some dots. I am more than a happy with the result
....but need to do more tests
Pennylane if it helps, I cooked the fume with a big soft reduced flame, like a big bic light, like 10 cm large and trying to dont touch the bubble with the candle.