I chalked on real slate for decades with no problem, so I don't know
where you get "easier" from. plywood is easier to cut and weigh a lot
less. The only disadvantage to slate is weight and cutting to size,
but even that's nothing to worry about in small doses.
Big advantage: When the kids are grown, use it as a sharpening stone.
You can cut it up and make boxes and sell it as oilstones, and more
than pay for slate and labour.
Possible source: Boards of education scrap schools, and you might be
able to scrounge a huge piece like I did.
I hear you, like the Dupont Freon thing. Thanks to Dupont we now have a
Freon that is more directly harmful to humans vs. from the scare of
depleting the ozone layer which was in worse shape in the 1920's. Shall we
talk about the mold industry now. LOL.
Exactly, about 18 years ago I was reading about the Freon fiasco on an
"uncirculated to the public" automotive trades magazine. Basically it was
mentioned that the Swill scientists had discovered back in the 1920's that
the ozone layer was in fact in worse shape than it is now, 1987 ish. Dupont
was pushing legislation to ban the old R-12 because it depleating the ozone
layer. Seems as though the real truth is that Dupont's patentent to
manufacture the Freon was getting ready to run out and they had this brand
new pattent on the new freon. Plus the new freon is supposidly more
directly harmful to humans than the old. That's probably why the new safer
freon must still be captured and not let back into the atmosphere when a
mechanic works on an AC system.
It has to be recovered because the EPA was getting pissed that people
were not recovering all refrigerants, only R12.
The 134A you buy for refrigeration is the same chemical that is in the
cans of compressed air for cleaning computers and such.
Rubbish. Until 1957 and the International Geophysical Year, we had
almost no knowledge of the upper atmosphere, the ozone layer, and
particularly its behaviour near the poles. One of the problems with
studying upper atmosphere behaviour is that we just don't have good data
in reasonable volume until the 1980s - there was no way to get
instrumentation in position to measure it, certainly not on a regular
It's odd that much of what we know about the upper atmosphere is
courtesy of NASA's second-hand U2-R, a relic of the Cold War, and also
that plate-tectonics and continental drift was only convincingly
demonstrated thanks to oceanic mapping efforts intended to hunt ICBM
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