Seven more colours tested today - I'm not quite sure why I chose these particular colours, they aren't the most inspiring ones I have ever seen.... But anyway, they all worked well.
I fired the Grey Blue from yesterday again at a much lower temperature this time and the result is much better - but even now it's not entirely even. Maybe it's just an odd batch.
Again - there are two layers (two firings) to each piece, with the colour sifted directly onto the copper.
This is a bit time consuming, but hopefully it will pay off when I need to choose colours for jewellery pieces.
Only one more opaque colour to go, then - the transparent ones.