Thanks, Mary Rose. I'll make a note of all this.
I talked to Tom Ellis about the various whites of Thompson Enamel. I had trouble with 1020 Titanium White and transparents cracking over it, as did Candy.
Tom told me Titanium White is not to be used as an undercoat. It is to be used OVER enamels or as a painting enamel.
Tom said other whites that can be used with enamels on top are:
1010 undercoat white
1030 foundation white
1040 [I don't know what this one is]
1045 antique
1050 matt white
1055 and 1060 can be used as white and with enamels on top.
Hope this is helpful.