Separators for moulds
It is important to put a separator on the mould -normally kiln wash – before using it. Once coated, ity will not need to be re-coated unless the surface is damaged, scratched, etc for a very long time. If the kiln wash seems to be rough you can smooth it in various ways as noted in this tip:
The advantage of kiln wash is that it does not cost much and lasts a long time. The thinfire or similar is a one-time-use product.
The binder in the thnifire burns away during the heat up and allows the now unbound separator to drift down to the mould before the glass begins to conform to the mould. In that way it is very similar to a fine dusting of kiln wash powder over the mould surface before firing.
In short, I don’t see the point of using Thinfire or similar during most slumps (I can see that there are rare occasions where this method would be advisable). You have to kiln wash the mould anyway. KIln wash is cheap and long lasting.