Sorry Peter
I thought I had answered this. Must be growing oldI have researched this a lot. From what I can discover, it seems that there is a critical point when mixing when colour and glitter is added. This may be obtained by checking the temperature frequently and try to catch the mix just before the setting time has been reached. Umfortunately, atmospheri pressurec and humidy have an effect. Still have a bit of a way to go yet .
Thanks for the offer of the blanks - it is appreciated,
Cheers
Frederick