Are tack fuse and fire polish the same thing?
They both occur in the same temperature same range, depending on the degree of tack fuse you want.
What you are doing in the fire polish process is heating the top surface enough to appear polished. Very little time is needed in a fire polish at top temperature as opposed to a tack fuse.
In a tack fuse, you want the bottom of the upper pieces to be hot enough to stick to the bottom layer. This requires a higher temperature or longer soak than a fire polish.
At around 730C, depending on your kiln, you will be softening the upper surface of the glass enough to give a polished appearance. To determine whether the polished surface has been achieved, you can peek into your kiln at the chosen temperature to see if the polish is complete.
This is also the temperature at which sintering, or a lamination of the glass pieces occurs. The edges will still be sharp, but cannot be pulled apart. This kind of fusing needs careful annealing – long soaks and slow cools.
Tack fusing of various degrees occurs in the temperature range from 730C to 770C. To determine which temperature and soak time will give you the result you desire will require experimentation and observation. Generally, you can achieve the desired level of fuse with lower temperatures and longer soaks, as you can at higher temperatures and longer soaks.
It is also possible to give a fire polish to your glass at a really low temperature, such as 550C, with a very long soak. This will avoid significantly flatening the surface of your piece. This is the effect of heat work.