Liquid something

The day I saw a saint’s blood become liquid

Apropos of nothing, the Catholic Herald has a description by a priest of his witnessing a decade ago the "marvel" (the Church does not formally acknowledge it as a miracle) of the liquefaction of the blood of St Januarius in Naples.

There is also a link to a helpful Wikipedia article on the saint, which gives some details of the research that has been conducted on the "blood". (The most popular scientific explanation is that it is a thixotropic substance - a gel that liquefies when agitated.) The simple matter of extracting a small amount and putting it in a mass spectrometer is not on the cards, apparently, but I was surprised to learn that a light spectroscope has been used a couple of times, including as recently as 1989. These results are said to be consistent with the vial containing hemoglobin.

Wikipedia also mentions that there are a couple of other saints' blood relics around Italy which liquefy, and apparently it doesn't happen in other countries. This does suggest that the answer lies in an Italian who came up with a neat thixotropic compound, and put it to innovative use in the 1300's, but it is unusual that this type of compound is not mentioned in science until 1863 (this is mentioned in the update following).

UPDATE: I see this morning that there is a really good, detailed report by what looks like an Italian skeptic group (although the tone of article is moderate). It details how there have been attempts, going back to last century, to make mixtures which behave like the relic. The "marvel" has been the subject of skepticism for a long time.