[Darkroom] Granite Counters

Jasmine Strong jasmine at electronpusher.org
Sat Feb 6 19:29:30 UTC 2010

You'd be surprised just how radioactive some granite countertops are.   
Some of it can be over 200 microroentgen/hr.  That's easily enough to  
fog sensitive films in just a few hours.  Since much of the radiation  
comes from radium daughters, there's a hefty gamma component and it  
doesn't even need to be in contact with the material.


On 6 Feb 2010, at 10:58, Chris Murphy wrote:

> This is just a guess, granite is nowhere near radioactive enough to  
> be a concern around film. The exposure time with direct contact to  
> granite would probably be months with high speed film. Again, I'm  
> just guessing.
> As a boy, I measured the radioactivity of granite buildings and  
> found no significant levels above cosmic and solar background  
> radiation. Smoke detectors contained americanium and were much more  
> interesting to measure.
> Apparently old lenses contain thorium and yttrium and even those  
> would take several weeks to expose ISO 100 film.
> We could intentionally expose ISO 6400 film to granite in a light  
> tight photo paper box and see what happens vs a clipping of the same  
> roll that has not been exposed. A Geiger counter could be used to  
> calculate a proper exposure time?
> Chris
> Sent from my iPhone
> On Feb 5, 2010, at 16:30, Jasmine Strong  
> <jasmine at electronpusher.org> wrote:
>> I'd be touchy about granite for a darkroom on the grounds that it can
>> be surprisingly radioactive and that this can fog film over time.
>> -J.
>> On Feb 5, 2010, at 3:46 PM, John Magolske wrote:
>>> * Kelly <hurtstotouchfire at gmail.com> [100205 15:37]:
>>>> Well, just to be clear on our options here, what are our  
>>>> requirements
>>>> for a counter surface?  (Ben?)  What are our other price options?
>>>> -Stainless steel (also not cheap)
>>>> -Formica (cheapest option--price estimate?)
>>> I've heard soapstone is ideal for chem-lab counter tops (more inert
>>> than granite, etc.). I'm not suggesting we should hold out for that,
>>> but if there happens to be a big slab of it laying around  
>>> somewhere...
>>> It's also easy to cut.
>>> John
>>> -- 
>>> John Magolske
>>> http://B79.net/contact
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