The tack fuse range is around 730C – 780C. This will give a graduation in profile from the very sharp, almost barely laminated, to one very rounded almost flat. Choosing the right heat for the right profile is one of balancing several elements: temperature, time, speed.
|Low temperature, high tack fuse|
If there were no other considerations, you could go slowly up in temperature and peek in at infrequent intervals until the right profile had been achieved. However this tack fusing is happening in the devitrification range, so slow rises in temperature are not advisable.
|Medium temperature, mid tack fuse|
So an alternative strategy would be to go quickly through the devitrification range (700C to 760C) and soak for a bit longer above that range. However, often the desired profile may has disappeared by the time you get to 770C.
|High temperature, rounded tack fuse|
It would seem that you can attempt to balance the temperature, time and speed equation by firing quickly (such as 330C/hr) to your desired temperature and soak there for 10 minutes only.
To ensure you get the profile that you want you should begin to observe from at least 10C below your chosen temperature. If you do not get the profile you want, you can extend the soak until the desired effect is achieved. On a subsequent firing, you can set the top temperature a bit higher, but with the 10 minute soak and again observe. This can be repeated until the desired combination is achieved.
Each of these attempts needs to be completely recorded so that the results can be used in later firings if slightly different profiles are needed.
Also look at this entry for annealing of tack fusings.