I enjoy playing Tibetan Singing Bowls -- easy to locate, check ebay
... or Google!!  Anyway, Mercury is frequently mentioned as a
component in the mixture of their metals.  We all know liquid mercury
is a serious toxin ... but then again "dental amalgam" is supposed to
be "safe".

I am concerned about giving these as gifts!
* How do I distinguish singing bowls which include mercury (or don't) and
what are the health risks?

A Researcher had a lock on this question for while.

A couple of points:  

The singing bowl you can buy will not be made of the 7 or 12 metal
alloy that has been found in antique bowls, which does contain
mercury.  A bowl that you can buy will almost surely NOT have mercury
in the alloy.

http://www.asianartmall.com/tibetansingingbowlsarticle.htm
http://9waysmysteryschool.tripod.com/sacredsoundtools/id6.html

Mercury is indeed very poisonous, so no one is going to speak up and
say that there are no risks, but millions of people with amalgam tooth
fillings, which contain mercury, are not all  - or any -  becoming
"mad hatters", although there is a "scare industry" to get them all to
have new fillings.  The fact that some dentists support this and
"test" clients and expound on the risks speaks for itself.

The fact that amalgam, which includes a much higher percentage of
mercury than that in an antique singing bowl, has not been proven
harmful, suggests strongly that the bit in the alloy of the old bowls
is also not harmful.

Mercury, which is liquid at room temperature, is said to very
volatile, that is, the liquid vaporizes rapidly  - one thinks about
the way gasoline or pure alcohol evaporate  - wow, scare! -  because
mercury vapor is the "best" way to suffer from mercury poisoning, a
serious occupational hazard for felt makers in olden times and for
people active in fire-plating gold, both processes that released
mercury vapor at much higher rates than at normal room temperature.

Here is a site that talks about vaporizing of mercury:
http://acc6.its.brooklyn.cuny.edu/~scintech/mercury/WhatBigDeal.htm

"Reported having 1 kg of mercury in a cauldron in a 43 m^3 room. He
did not seal his package of mercury. The typical cauldron is about 25
cm. in diameter, and with an air exchange rate in the room of .5 air
changes per hour, the mercury vapor level is approximately 600 ug/m^3.
This level is twelve times higher than the accepted occupational
exposure limit set by the U.S. National Institute of Ocupational
Safety and Health."

Note the cauldron dimension for his 1 kg of mercury.  It has a surface
area of 490 sq cm.  Mercury is 13.593 times heavier than water.  If he
had 1 kg water  in that container, it would be about 2 cm deep, but he
has mercury, so it is only 2cm/13.6 deep, about 0.15 cm deep, 1.5 mm. 
The calculations in the excerpt are all correct, but the premise of
someone keeping a kilo of mercury as a thin layer at the bottom of a
25 cm (10 in.) diameter cauldron is nonsense.
Someone is trying to make an argument.

Of course, this is no professional advice (see the disclaimer below),
and I will admit that I have had amalgam fillings for over fifty years
and that as a kid I played with pure mercury, holding it in the palm
of my hand and rubbing it on dimes (then silver), making them shiny
for a while.  So, yeah, as everyone can attest here, I am pretty goga.
 ;)

The important point to your question is that the bowls you can buy
won't have the alloy of the the antique ones that contains mercury.

Myoarin

Hmmm?  Yeah, maybe I am:  that should be "gaga" ...

Hmm.  A researcher had a lock, but then...?

Anyway thanks, Myoarin-ga, for the adoption and lengthy detailing of my issue.

For a bright guy, I hate to suggest the comprehensive elements were
lost on me but I have to address specifics -- the most compelling
evidence of non-exposure is MITCH NUR's interview response asserting
that modern bowls are by-and-large brass-only, correct? After all the
repetition of sales-pitches suggesting multiple "unknown" metals,
these statements are all just borrowing the reputation of the classic
ingredients because nobody uses anything other than "bell-alloy"?
(Nonetheless, it IS a great link!)

Alrighty then... and I must confess the vaporization issue was
somewhat lost on me; perhaps I've just a had a long day but I assume
you are saying that only mercury vapor is harmful -- to which one
would not be exposed without a) liquid mercury or b) deliberate
heating?

Anyway, thanks for the response(s)!

Hi Kajagoo,
I think you understood the information correctly, especially about
modern bowls being made of simple bell alloy.  Personally, I expect
that the complicated antique alloys had just unintentional traces of
the many ingrediants, probably just contamination that was common from
the primitive methods of refining and probably unkown to the makers.

And yes, my understanding (no expert) is that mercury vapor is the
most likely form of poisoning, also ingesting it in some way, but
these days that is rather rare.
I should have posted this site about mercury poisoning before:
http://www.calpoison.org/public/mercury.html 

It is interesting that "calpoison" after explaining that ingesting
elemental mercury is probably harmless goes on to such a song and
dance about avoiding any skin contact with the element. But as I
mentioned before, no responsible source can down-play the risks.

So give all your friends bowls.  Buy them at once so you can pick ones
that harmonize, and then you can all join to have concert.  :)
Regards, Myoarin