[Darkroom] Granite Counters
jasmine at electronpusher.org
Sat Feb 6 11:29:30 PST 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?
> 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.
>> 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
>>>> 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
>>> It's also easy to cut.
>>> John Magolske
>>> Darkroom mailing list
>>> Darkroom at lists.noisebridge.net
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