Thorium & Radiation: There is a Light That Never Goes Out

By sheiler on
face painted on a wall in paris

What’s in Your Grandma’s Candy Dish?  Interview with a Citizen Scientist

We noticed some tweets by a fellow named Conrad Knauer, boasting yard sale finds that he described as being ‘clicky’. One candy dish led to another ceramic green cat, which led us to reaching out with him for a chat.  We thought we’d share here.  

Outfitted with a portable, USB-powered Geiger counter and UV flashlight, Conrad Knauer spelunks for signs of clicks inside antique shops, thrift shops, and at yard sales in Saskatoon Saskatchewan (Canada).

The New York City native earned a degree in Biology from the University of Saskatchewan, and ended up staying there to raise two children.

My kids like to help. My daughter is 9 and son 5.  They have both spotted objects for me that tested positive (for radiation); they both know the particular tangerine orange of uranium glaze and my daughter has an eye for the green of uranium glass.

Knauer’s hobby began when Stuyvesant High School, where he attended as a student and also worked for the chemistry department, was in the midst of relocating to another building.  Knauer got his hands on a few items the school no longer needed including a “boxy ‘60’s green Geiger counter that pugged into the wall”.

Fast-forward a decade later

log to wired magazine

After reading the Wired article, “Uranium Is So Last Century — Enter Thorium, the New Green Nuke,” and then watching the video “Thorium Remix 2011” Conrad Knauer found himself “bit by the Thorium bug…that got me tweeting (evangelizing?) about it. Perhaps a little obsessively ^_-;”.

Fans of Thorium, and the number seems to be growing, state how the liquid-fluoride thorium reactors (LFTR) “have the potential to not just generate less waste going-forward, but consume existing stockpiles of waste.”

The LFTR design concept absolutely captured my imagination; that they had a working molten salt reactor back in the ’60s is astounding.

Knauer then checked the US EPA website listing of the types of objects that typically carry radiation.  He knew about smoke detectors, but learned that:

  • Certain radioactive materials were used in antiques because of their unique color.
  • Antiques that contain radioactive materials are usually not a health risk if they are in good condition.
  • Antiques containing radioactive material can continue to emit very low levels of radiation for thousands of years, if not longer.

A handheld Geiger counter would be able to read these low levels. But Knauer had lost track of his original large Geiger counter, so when his brother asked him what he wanted for a gift, he requested, and received, the GMC-300.

geiger counter, camera-lens

This he keeps plugged in to his car lighter so that he can track the radiation of an object or even air, at a moment’s notice.  He also keeps handy a UV flashlight (easy identify uranium glass) and takes short trips around Saskatoon to find the unusual and whimsical that click.

Clicky defined

Units of radiation come in the form of Sievert (Sv),

“…or micro-Sieverts per minute. What is actually detected is an electric discharge inside the GC’s tube caused by the ionizing radiation.”

The Geiger Counter shown above displays CPMs – “counts per minute” and makes a clicking sound (“the clicking being typical, going back many decades”).

One of the antique dealers knows about uranium glaze/glass, radium dials, etc. and if I stop in his store will show me things he thinks I might want to buy (sometimes I wish I was made of money! ;), but normally I find objects on my own.

Thrift shops aren’t testing for radioactivity and some of these things look like just another piece of bric-a-brac (also, there are a lot of non-radioactive things that can look very similar- i.e. orange glazed ceramics, green glass or clock dials- and need to be tested to be sure). My most recent find was unusual and not obvious at all: (only mildly radioactive, so had to test for a few seconds and it didn’t fluoresce green in UV)

Still, they know me at all the thrift shops, yes, because I like to show them what I’ve discovered and talk (sometimes at length) about the objects.

Shelflife of Homelife

Conrad Knauer’s girlfriend, has been largely supportive of his habit, even buying him an appropriate vanity license plate.

image of kids near a car with Thorium on the license plate

Daddy can I PLEASE play with the toy next?


Below are some highlights of his finds:

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Another Surprising Find

Amusingly, I once found a *person* at a thrift shop! She walked right past me and the kids in the toy section and my GC spiked fairly high. I walked over to her and glanced in her cart, seeing only some clothes and shoes (so nothing obvious that should be radioactive), but by then my GC started its warning chirp (default is 1000 CPM). I then correctly guessed what was going on- I mentioned that she was setting off my geiger counter and politely asked if she had received nuclear medicine recently- she said yes, she had 🙂 I think it was a scan, so with

While he doesn’t have a precise number of clicky items in his collection, Knauer says he easily has at least one hundred radioactive things.

I slow down on a particular item once I have several, which includes clocks, depression glass (yellow and green), orange and yellow glaze ceramics, smoke detectors, gas mantles, cameras, lumps of potash (potassium is weakly radioactive; 20kg sodium-free water softener sacks from Safeway definitely set off the GC).

Knauer admits his girlfriend has been known to “roll her eyes at this a bit.”

He’s agreed to limit his spending to $20 a week, which he found was easy to stick to.  He’s been able to find items as cheap as 10 cents, or even for free:

“A couple times I’ve been given thorium gas mantles after just talking about them (as in, ‘ah, it’s radioactive and you collect them? please take it’). I try to reassure people they’re not overly dangerous though!”

Some benefits advocated by Thorium enthusiasts/LFTRs:

  • Safer, cleaner, and ultimately cheaper than uranium
  • Much harder to use in nuclear weapons, and therefore limits the proliferation risk
  • Ample supplies
  • No melt downs since the normal state is already molten
  • Doesn’t sacrifice the environment
  • Could provide the world’s energy needs carbon-free for a thousand years.


Shorter Ted talk:

Muuuccch Longer:

Stayed Tuned for Part 2

Next time, we will go into some detail about safety, and school projects involving radiation.

You can follow Conrad’s tweets here: @ConradKnauer.

You can also follow Professor Blue on twitter: @ProfBlue

…And If You’d Like Your Own Private Geiger Counter…




  1. Do you know anything about the glazed ceramics sold in the 50s & 60s at Knott’s Berry Farm California when Mr Knott owned it? They glow in the dark if they have been exposed to light. We would be brought into a room full of them and then the lights were turned off. They glow multiple colors predominantly yellow while, orange and green. I have 2 and can’t find anything like them online.

  2. Hi Jackie,

    Interesting question. I don’t know since it’s not my hobby, but I’ll touch base with ConradKnauer to see what he knows!

  3. Hi Jackie! I hadn’t heard of that before, but I did a little searching and found
    “LUMINESCENT CERAMIC GLAZE […] is based on the alkaline earth aluminate for main content as raw material. This inorganic products after absorbing visible lights for 10-30 minutes, They will glow in the dark at least 12 hours. They are none of toxic and free from any radio activity and with widely used.”

    and has some pictures

    The phenomenon is based on and the ceramics won’t be any more radioactive than usual (all ceramics are a little bit radioactive from naturally occurring Uranium, Thorium and Potassium that was in the clay they were made from).

    An interesting historical footnote: discovered radioactivity while investigating Uranium’s phosphorescence.

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