[Darkroom] Granite Counters

Chris Murphy chrisnoisebridge at gmail.com
Sat Feb 6 20:12:10 UTC 2010

I was suggesting direct contact because of the weakness of the ray  
dropping to infinity over the distance of an inch or two. Gamma or  
not, I'm pretty sure it's just too weak.

A more practical concern for granite is that it's heavy and expensive.  
Any old counter will work in a darkroom in my opinion. If holography  
is on the agenda, then we would need/want a more specialized optics  
table. This would be far more interesting to me than a traditional  
darkroom (as I've pretty much gone all digital).

Sent from my iPhone

On Feb 6, 2010, at 11:29, Jasmine Strong <jasmine at electronpusher.org>  

> 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.
> -J.
> 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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