I have put up a new version:
http://www.shorlandsite.com/images/Shorlands,%20Humbers,%20Fire%20&%20Trakmark%20Article%202016-v2.pdf
The problem was I conducted these tests in the summer then lost my records for the temperature, so relied on my memory.
I have since found the records, yes on the back (& front) of an old envelope! I have adjusted the temperatures accordingly.
I had forgotten that I managed to get the Trakmark up to 300 deg C & it still didn't drip or collapse, just went hard & crusty.