Thank you all so far
I have been putting 3 coats of the underglaze on, and perhaps I need to put a thicker glaze covering on - I've just been doing a quick dip - but I will try more of all.
I am also going to add some 3134 Frit to the underglaze, and then on another add some Gertsley and do test pieces. (as well as thicker applications of both under and clear glazes)
Any more ideas welcome!