Kaolin is also used to trigger blood clotting through the 'contact pathway' or 'intrinsic pathway'. The original experiments on this were performed by the anatomist William Hewson in the 1770's where he ran freshly let blood into containers of china, or gutta percha and observed the different coagulation times. It wasn't till the 1880's that they discovered that bloodd clotting is usually triggered by constituents outside the blood (the extrinsic pathway) with the prime activator, tissue factor (as a preparation including lipids called thromboplastin) identified and described by Morawitz in 1905 in a somewhat extensive review (1)
(1) Yes I have seen a copy. It is in german as it was published in Angewandte Chemie. Of particular note are two things. a) all the references are listed at the start. 450 or so of them. and b) a particular figure (diagram) is not included. This is interesting as it is frequently seen in historical reviews attributed to this paper, clearly by folk who have not read it. There was an English translation in 1952 which I have not seen which may have this figure.
OK, I learned this when I wrote my PhD thesis 'My life in the laboratory with a bunch of clots' 24 years ago.