Enamelling reds

[Bohemianchick23]

Hello
I'm struggling to get transparent reds to fire red. They are a orange brown. I have tried playing around with the temperature, no joy. I tried firing on top of Keum boo gold and clear flux, no joy. I have ordered C1 gold flux which is meant to help. I'm using fine silver that has been cleaned with nitric acid before
hand. Has anyone got any tips?
I contacted vissum signum, who said to stick to the firing temperature and go in short and fast. Still didn't seem to work.
Has anyone any experience enamelling plique a jour on 18ct gold? Any tips please?
Any help appreciated. Orange and yellows behaving, as are opaque reds, just not the translucents or transparents reds.
Sarah