I’ve seen this story a few times over the years, but have never seen an adequate explanation. I’ve checked the archives here, and searched snopes.com - but no dice.
So, I present the question to the great minds of the SDMB: What’s the deal with the blood?
Possible theories:
an environmental effect from being handled at certain times of the year
unseen tampering by those in on the trick (the church?)
The effect of St. Gennaro’s blood has been convincingly replicated in a laboratory, using a thixotropic gel of iron hydroxide, colloidal FeO(OH).
This mixture solidifies and appears dry when left undisturbed, but liquifies when moved, even slightly.
It was possible, in the fourteenth century, to create a substance very close to this - that is, all the tools and procedures seperately existed, although there is no no explicit evidence of any chemist – or alchemist - having actually done it.
I express no opinion on whether the substance displayed in Naples is miraculous blood, or a thixotropic mixture of limestone and molysite.
An article appeared in the Journal of Scientific Exploration in 1992 which attempts to explain the event and discusses some of the disasters that occurred in those years that the blood did not liquify.
Er, no. I just saw a special on Discovery or TLC about this phenomenon (as well as other “miracles”), and it stated that the Church will not allow testing of the substance. It remains sealed in that glass bulb all the time.
The show covered the thixotropic compound angle, and also the possibility that it is simply a colored wax-based substance, which become liquid when heated by the body heat of the priest holding it, and the throngs packed into the church.
Actually, the notion that the blood of St. Januarius (“Gennaro”) and of ther saints being due to thixotropic fluids goes back well before 1992. As I pointed out in a letter to The Skeptical Inquirer circa 1992, the idea had been proposed in a textbook on thixotropy published in the 1950s. I don’t have the reference with me now, unfortunately, but it’s given in my letter (under my real name, Stephen R. Wilk). The author showed the locations of such vials of “miraculous” blood on a map of Italy, upon which were also plotted locations of deposits of the fine iron oxide that would be needed for the thixotropic preparation. There’s apretty good match.
It seemed to me that a good “clincher” fr this argument would be to find pre-Christian legends of “miraculous” blood of the gods or heros from Roman mythology, but I haven’t turned any of those up yet.
If such an unpronounceable substance liquefies whenever slightly disturbed, then how does one know that it’s a solid at other times? It seems to me that the easiest way to tell something is solid (espescially when it’s sealed off in a jar) is to disturb it and see if it moves.
Also, there are a few tests, at least, that could be performed without opening the jar or altering the substance-- Density comes to mind, for instance.
The vial (actual vials) containing Januarius’ blood is kept sealed away most of the time. Only on special occasions is it brought out and viewed. At those times (less often than once per year, I think) it is only handled by the priest. They have not been very cooperative in letting it be examined, so I don’t think an absorption spectrum has ever been taken, even though it could be. Similarly, an investigator would have a hard time getting his hands on it to heft it, let alone weigh it.
There have been a couple of books on the phenomenon, mostly by pro-miracle folks who publish lists of temperatures in the cathedral in an effort to show that the effect is NOT due to temperature (these books are circa 100 years old, and predate suggestions of thixotropy).
Have a look at D. Scott Rogo’s book “Miracles”, for a description of the ceremonies. But read it with more than a grain of salt.