Luminous Watch Dial Risks
Table of Contents
Types of Luminous Dials
Identifying Luminous Dials
What Are the Risks of Radium Dials?
Many vintage watches, especially military watches, have gold or
whitish colored "paint" on the hands or on the numbers on the dial.
This paint is quite likely made of a phosphorescent compound mixed with
This causes, or at least used to cause, the numbers and hands to glow
in the dark. Unlike many glow-in-the-dark compounds, these would glow
all night long and would continue to glow for years on end. After a while
(25-50 years?) the paint will be destroyed by the radiation from the
radium so chances are these watches will no longer glow in the dark.
The radiation from these radium dials have the potential to cause
various health risks and should be handled in ways to minimize these
risks. I am not an expert in this field, but I have tried to collect
as much information as I can so that you can evaluate how you want to
deal with these dials. Corrections and suggestions are very welcome.
Besides radium, there are several other methods of making "glow in the
dark" watch dials. There are various non-radioactive phosphor compounds
that will glow in the dark after being exposed to light. Some modern
compounds can glow for 10 to 15 hours after a relatively short
exposures to bright light. Tritium, like radium, is radioactive, but
it is much safer. Tritium, a form of hydrogen, has a reasonably short
12 year half life so it doesn't have the long term dangers that radium has,
and it decays into harmless helium. The beta particles that tritium
gives off can not even penetrate the outer layer of dead skin on your
body, let alone the watch crystal and watch case.
There are three primary ways of identifying what kind of luminous paint
is on a dial.
First, beginning in the 1950s or 1960s, watches that used tritium
would either have two small "T"s on the bottom of the dials by the 6
or have "T<25" labels. The "<25" means that there was
originally less than 25 milliCuries of radioactive tritium. Watches
that used radium would similarly be marked with an "R" or "Ra". This
technique will not work to identify earlier watches.
Secondly, you can use a dosimeter or a Geiger counter to measure the
radiation levels. Radium will show up, but tritium and
non-radioactive glow in the dark compounds won't. Apparently, the
emissions from tritium are so low in energy that you need special
detectors to even measure it.
Finally, and maybe the most common way, is to judge the age of the
watch or clock. Based on the age, a reasonable guess can then be
Luminous radium dials were first used around 1910 before the dangers
of radioactivity was fully understood. Radium dissolved in water was
even sold as a health tonic and said to increase your energy levels
and cure diseases. After WWI and through out the 1920s, radium dials
became popular and were widely used on watches and clocks. In the
late 1920s, it became obvious that the girls and women who painted
the dials were suffering and sometimes dying from health complications
caused by the radium. The widely published liability trial of the "Radium
Girls" caused the popularity to wane in the 1930s, but radium
dials were again used widely during WWII.
The vast majority of watches or clocks made before 1950 that have a
thick yellowish or white paint on the hands or dial are made with
During the 1950s and 1960s, the dangers of using radium was recognized
and it was phased out in the US. Instead, either non-radioactive
phosphorus compounds were used or various tritium compounds were used.
Other countries, especially third world countries, still use radium.
For example, Iraqi tanks captured during the Gulf War had radium dials
In the last decade or so, tritium has also started to be phased out.
Despite its lower risk compared to radium, it is still radioactive
resulting in more red tape. The non-radioactive modern glow in the
dark paints are often considered to be a better solution.
I have never gotten an explanation of exactly how risky these radium
watch dials are from someone who I would judge to really know what
they are talking about. Many people have a little knowledge and make
claims that range from "immediately call your hazardous waste disposal
people", to "hey, watchmakers have been cleaning these watches for
decades, and there isn't any signs that this is any more dangerous
than crossing a street."
The primary health risk of Radium is that it is radioactive and if it
is ingested or if dust particles containing radium are inhaled, it can
lead to various bone diseases and forms of cancer. While there is no
safe level or radiation exposure, everyone is exposed to a certain
amount of radiation every day. The question is: "are the levels of
radiation from the radium dials high enough to worry about?"
Not all the radioactive material remains where the paint is visible.
Over time, this paint will become very dusty and it is important not
to breath any of this dust. The watch crystal should not be removed
without a good reason, nor should the watch case be opened up. The
dust is due not only to the normal aging of the paint, but also
because when radium breaks down, the force of emitting the alpha
particle during the radioactive decay causes the daughter atom to
recoil. This recoil is strong enough to break the chemical bonds that
holds the atoms in place. The resulting daughter atoms will move a
little ways away and then settle. These daughter elements, such as
radon-222, polonium-218, lead-214, and such, are all radioactive and
just as much a problem as the radium.
In the 1920s, radium dials became popular enough that many companies
started producing them. They would hire girls and young women to
paint the dials and they were encouraged to lick the tips of the paint
brushes to get a sharp point. The whole environment in some of these
factories was very lax about the radium. The women would sometimes do
things like paint their teeth, faces and nails with this
stuff to surprise their boyfriends. Many of these women would later
develop health problems and some even died due to ingesting radium.
If you do a web search on the
you will find lots of stories on them. Many of these
stories are nearly identical, but one of the
articles is by Bill Kovarik.
Now, this might sound very frightening, but these women ingested a LOT
of this paint, "only" a few died, and probably not more than 20%-40%
had health problems. It is not clear how many of these health problems
were due to the radiation or due to the heavy metal poisoning. There
are lots of risky activities in this world, from crossing the road to
eating fatty meat, that most people don't think twice about
doing. However, people seem to panic as soon as you mention radiation
or "mad cows disease".
On the other hand, ingesting this radium may be significantly less of
a problem than breathing it. Ingested radium will either pass through
your system, or act chemically like calcium and enter your very slow
growing bones. The
CDC's Radium webpage
says that 80% of ingested radium will pass directly through you and
some of the rest will eventually be filtered out by your kidneys.
Radium dust in your lungs, on the other hand can stay there and
potentially cause lung cancer.
One particular concern of radium decay is the daughter element
radon-222. Radon is a noble element so it won't chemically rebind and
it is also a gas so it will float away from the dial. Radon has a
half life of about 4 days, which is probably enough for it to diffuse
to anywhere in the watch case but probably not long enough to escape
before it decays. The daughter elements of radon-222 are radioactive
solids, which will settle on the watch parts. So, it seems likely
that a watch with a radium dial will cause the entire movement and
inside of the case to be covered with a very find dust made of
radioactive material. Again, I am not an expert here, so this may or
may not be a real problem, I don't know. I've, however, read
discussions about how entire boxes and cabnets have become radioactive
due to storing small amounts of radium in on spot.
Now it is true that as time goes on, the break down of the radium will
cause it to lose some of its potency. Unfortunately, the half-life of
radium-226 is about 1600 years, so these watches will be about as
radioactive 200 years from now as they are today. For all practical
purposes, these watches will be radioactive forever.
One final comment on the possible health risks of radium is that the
dial painting companies weren't exacting in their formulas. It
wasn't just radium-226 that was used, but a variety of different
radioactive elements. Most of these other elements will decay faster
than radium-226, so they may be less dangerous now. Also,
depending on how the paint was mixed up, some dials were very hot,
while others were not. If you are concerned about a particular watch,
you should have it measured. Anything else is just a guess.
While the risks described above are as accurate as I know how to make
them, it is probably best if you evaluate the data yourself. The
following are some of the sources I have found on this subject.
A little more information on radium can be obtained from the
Radium webpage. However this page deals more with Radium in the
ground or drinking water rather than watches.
says that while the alpha and beta particles are
easily stopped by the crystals and cases, these dials also
produce many gamma rays. Many of these watches give off
20 mrem/hr in gamma radiation through the crystal, and some are as high
as 100 mrem/hr. You get a certain amount of radiation as a normal
part of life, typically around 250-500 mrem per year, so
according to this reference, you can easily double your radiation
exposure by wearing a radium watch for just a single day.
Yet another reference,
published in 1974 in 'The Journal of Chemical Education", talks about
how to remove the radium from watch dials for use in class room
demonstrations. It states:
"Treat the radioactive materials during procedures with
thoughtful respect and your maximum exposure dose per clock face or
compass dial will not exceed 1 milli rem. The hazards of radiation of
this amount are far less dangerous than the dozens of toxic, caustic,
and corrosive chemicals that students handle in a school year.
Somehow, I suspect that one of these two references is wrong.
There are several articles on radium dials in the
usually an excellent source of information.
In the June 1988 issue (vol 30/3 num 254 page 225), there is a short
article by Robert Free of the Texas Department of Health, Bureau of
Radiation Control. Two relevant quotes are:
Individuals manufacturing the jewelry [made from old watch parts] are
exposed to dusts containing radium from buffing and brushing exposed
watch faces, dials and hands. As a result, they run an increased risk
of cancer from ingestion and inhalation of radioactive particles.
People who repair and refurbish old watches are also at risk. In
addition, contamination of the workplace is a serious problem.
Decontamination can cost thousands of dollars.
Texas is one of many states which has adopted rules prohibiting the
use, possession, manufacture and distribution of radioactive material
without a license. That includes the distribution of radium contained
in costume jewelry and watch parts.
In an article from December 1974 (vol 16/6 num 173 pg 754),
Henry Fried basically says that the luminous dials that use tritium
are very safe and that unless you are have clock from the 1920s or
1930s, you almost certainly don't have a radium dial. Henry Fried is
a noted author of watch books, but I don't know if he is also an
expert on radiation. The article sounds very reassuring, but he never
actually says that radium dials are safe, dismissing them as being
almost non-existent because there is no "R" by the dial of most
watches that he has seen. Unfortunately, I don't think the "R"
marking for radium was used until the 1950s or 1960s.
Then there is a series of three short articles on the subject. In the
first article, from December 1984 (vol 26/6 num 233 pg 732), it is
reported that a luminous radium dial on a wrist watch was measured
with a dosimeter at 12 mrem/hr. It was noted that individuals
working with radiation are permitted a weekly does not to exceed
100 mrem/wk and caution was advised when handling and wearing
In a reply to the above article, published in the Jun 1985 (vol 27/3
num 236 pg 336), it is claimed that just measuring a watch at the
crystal is misleading. The 100 mrem/wk amount detected by the badges
worn by nuclear workers assumes that the entire body receives that
dose and a point source like a radium dial is much less dangerous
because it effects a much smaller area. It is calculated that you
would need to cover your entire body with 3000 wrist watches emitting
the 12 mrem/hr to make it equivalent to a nuclear worker receiving the
12 mrem/hr. Although it wasn't calculated in the article, if you take
the difference in area into account, this would make the watch
equivalent to receiving less than 0.7 mrem/wk.
It was also pointed out that different parts of the body can safely
take different amounts of radiation. The hands and wrist, it is said,
can safely receive a maximum of 19 rem/quarter. Although it wasn't
calculated in the article, This is equivalent to about 8 mrem/hr. So,
while this article is very dismissive of any risks associated with
radium dials, in fact, the figures they give show that if you wear a
wrist watch with 12mrem/hr on one hand for 16hrs a day, you are right
at the maximum safe exposure for your wrist.
In the December 1985 bulletin (vol 27/6 num 239 page 729) there is a
third article on the subject. It claims that the math in the
second article is wrong. Furthermore, as was pointed out in the first
article, some people wear wrist watches 24hrs a day and often
sleep with the watch resting against their head. In this case, a
dosage of 12 mrem/hr is far in excess of the recommended maximum for
the head and eyes. Likewise, pocket watches worn close to the groin
or pendant watches worn over the breast would both be of concern.
One watch oriented source is
TimeZone's article on
Luminous Watch Hands.
While this source sounds fairly reassuring, it leaves out any mention
of the gamma radiation generated by the Radium hands and leaves out
the fact that Radium decays into Radon gas, which can spread
out to leave radioactive decay products all over the watch.
Another watch collector,
radium levels on his Hamilton "Whitney".
The radiation levels were enough to convince him to have his watch
redialed to remove the radium.
Finally, while it doesn't discuss the risks of radium dials much,
there are some interesting pictures of luminous dials at the website
Alan's Vintage Watches:
Microscope Images of Radium Hands
Radium Watch Dial
In summary, I think it can be said that:
- These radium dials aren't going kill you instantly, or even within
a few years.
- These dials have a very real risk associated with them.
- You should never remove the crystal or open the watch case unless
you have a good reason.
- You should probably not sleep with a radium dialed watch on your
wrist. It may be convenient to be able to check the time in the
middle of the night, but it is probably a risk you can easily
- Since the radiation levels of radium dials vary so widely, if you
are going to wear a particular watch a fair amount, it is probably a
good idea to use a dosimeter to measure how radioactive your
particular watch is.
- If you are working on these watches, you should be very careful
not to stir up the dust and to not contaminate your work area.
- If you need to deal with these radium dials on a regular bases,
you should learn a lot more about them than what can be found on this
web page. I am not an expert, I am only trying to give people a start
on learning about radium dials.