Temperatures for enamels
774C is far too high for enamels. Most glass enamels mature at 520-580C. Anything over that and they begin to “fade”. If you need to fire so high for the glass, then you need two firings one for the glass and another for the enamels. Also you need only a stablisation hold at the top temperature. I use one minute. Some do not use any hold at the top temperature.
Another possibility is to use ceramics on glaze colours that fire in the 780 – 850C region. They tend to be opaque though.