Copper glassline pen

[Laura S]

Hi
I'm struggling with firing copper Glassline. I applied the Glassline straight from the bottle, with one of the metal nibs. It looked fairly thick on the glass. However, after firing it looked totally washed out. No real colour to it all. I have tried putting it in between two layers of Tekta and on the capping layer of Tekta. I have shaken the bottle until my arm nearly fell off, so I really don't think that is the problem.
The firing programme I used is
222d to 677d 40 mins
333d to 785d 30mins
AFAP to 482d 90mins
56d to 371d

I know the advised firing range is 790d - 820d but my kiln fires quite hot and if I go to 790d I tend to get dog boning. I should say I don't have any problems with other Glassline colours.
Any suggestions?
TIA