From: REMOVE_THISdwilkins@means.net (Don Wilkins)
Subject: Re: Pink vs. Black Granite plate
Date: Sat, 24 Apr 1999 13:06:33 GMT
On Thu, 22 Apr 1999 11:57:28 -0400, Paul Koning <firstname.lastname@example.org>
>Jim McGill wrote:
>>> I don't know any specifics, but I do have an observation. My father's
>>> metrology lab was full of high grade surface plate type tables, all of
>>> them black granite. Also, the working surfaces and ways of his Zeiss
>>> 3D coordinate measuring machine are all black granite.
>> I think chemical stability may be part of the criteria. When I worked at
>> Tektronix we had black granite in the Metals and the Chemistry lab but the
>> machinists used pink. I asked one time and was told that the pink was better
>> but much more susceptible to acid damage (apparently it is slightly porous
>> and the acid can get down into the surface and pop bits out), so anywhere
>> that people were likely to have strong acids (like etching Metlab samples)
>> they used the black, but where there was only oil and solvents present they
>> used the pink.
>Interesting. Hadn't heard that. It doesn't apply to the lab I
>anyone who would have dared show up in there with anything caustic would
>have been summarily tossed out the door (or, possibly, the window!)
Most chemistry labs used Alberene Stone which is(was) a trademark for
a natural soapstone. It is dense, tough, homogeneous and highly
resistant to acid and alkali. Primarily a Magnesium silicate. Density
185 lbs/cu ft; fusion point 2200-2300 F; water absorption 0.075-0.15 %
in 48 hours; dielectric strength 37-70 kilovolts; transverse physical
strength 3000 to 3400 psi.
Yes you can etch out the surface with constant exposure to strong
acids. I never saw pink bench tops in a chemistry lab.