actually there is a lot more too it than just the heat. try this.
1) dont overheat the rod before picking up your frit, overheating will lead to problems. I could get into the rad details of this but I'll hold off for now. I usually hit with a larger flame, then back it off to inner flame right before i dip.
2) hold the rod way up in the upper flame were its mostly oxy, pointing the frit "almost" straight back into the flame. If you point it directly down into the flame it can boil the frit or fuse hase back into the clear, you want it to "wipe" the haze off so the frit becomes instantly clear.
3) immediatly angle yourself for an implosion, but only implode it 1/3 of the way so its a rim with a dimple in the middle.
4) hit the center briefly to bring the center dimple out. don't take too long with this, as at this point the outter rim is cooling.
5) dip into a backing frit and melt in at the same distance/angle/heat you did the implosion.
6) repeat #5 one or two more times depending on preference. you MUST retain heat through the whole process, any more than a 3-4 second delay will change your outcome. beyond 8 seconds and all you can hope for is a severely halo'd implosion.
7) flatten the back with a paddle while spinning. 2mm is usually enough, you don't want to flatten the piece. I could get into this more but not now. just retain as much of the maria as possible.
IMMEDIATLY cool your piece. if its 1"x1/2" (dia/depth) or larger you need to blow on it directly on the backside... like... almost passing out. the consistancy and penetration of this cooldown is actually the most important of the seriously important steps. once the glow is gown, look down through the edge of the topside of the maria. You should see ice blue and yellowish splotches. This is actually the base of the implosion that has hazed the tiniest bit as it tried to ion-swap with the backing frit and failed becuase of lack of germanium (alaskan thunder is a great backer). THE IMPLOSION SHOULD BE ALMOST COMPLETELY INVISIBLE.
9) Now carefully flamecut off your rod on an angle so the flame is pushing the heat up and away from the cab. remove the chunk left on the cab in the same fashion, don't ever point your heat directly down into the implosion. Your implosion should just now start to be striking to purply/browish/redish.
10) from underneath(backside) your flame finish off your front maria. You have about 10 seconds max to do this or you heat up the implosion too much and it will overstrike to icy halos.
11) IMMEDIATLY cool it down by blowing on it. Blow on the edge while spinning. Alternate to the top. your heat is traveling from the top to the bottom. you want it to hit the center and stop/cooldown.
12) if you made a good punty to your maria then you can just lightly heat up the puntymark and then blow on it to prevent the heat transfer... this one is realllllly important. If you have to heat it up too much to melt off the punty mark you could botch the whole thing. after its able to cool down for about 15 seconds or so you can add a loop or whatever.
I hope this helps.
I am actually in the process of writing a book that will include this whole thing in brain melting scrutiny. down to the chemical process of ion exchange and temperature balancing/bouncing.
vega-