On 18/12/13 04:53, DoN. Nichols wrote:
On 2013-12-17, dpb wrote:
On 12/17/2013 12:19 AM, DoN. Nichols wrote:
[ ... ]

Not saying anything about the mechanism, but it *does* happen.
Here is a report (from some not very specific time in the past):

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I've got some new old (Co-op brand, even ) Al paint still around --
so I went and looked at one. There's nothing on the cans about not
shaking. I've not used a lot but did a little touchup with one a few
years ago. AFAICT they're still as good as new despite the age as far
as appearance in can and behavior in use goes. I didn't drive to town
to put one on the paint-store shaker but I did put it on the homebrew
vibrator I've cobbled together here out of an old combine pittman sickle
drive. It's not as fast and has a longer stroke compared to real shaker
but does get the stuff off the bottom...I don't remember noticing any
pressure after that when opening it (but then again I wasn't looking for
any as had never heard the stories/warnings).
Well ... the experience my friend had would have been in the
early 1960s, I think. (I never asked him, but he had a summer job in
the hardware store at the time, and I knew him first a few years later
at work.

And I've never seen a label on the paint warning about shaking
it, but I *have* seen such a warning label about aluminum paint on a
paint shaker bolted to a vertical floor-to-ceiling I-beam at work (a
later job) This was one of the kind which cranks two flat plates down on
each end of the can and shakes it around a horizontal axis through the
middle of the can half way between the two ends.

I've got a tin of cold galvanising paint that carries the following warning

"CAUTION
care should always be taken when removing the lids of tins containing
metallic paints as these are liable if contaminated (eg by moisture) to
a build up of pressure during storage.

DO NOT SHAKE

Open carefully, preferably shielded under rags, especially if the tin
has been allowed to stand part full. Apply with dry brush"

The tin is also the only one I have seen that came supplied with 2
spring clips to hold the lid in place.


I don't know if there is more than one type of Al paint where there's a
significant difference in the makeup or not. I'd guess these go back to
around the late '70s/early '80s --
While his experience was (as mentioned above) likely in the
early 1960s.


[ ... ]

I'd like to see a real explanation--a quick search on manufacturers'
sites didn't bring anything to light.
I would too. But the one about the "tung oil" makes a certain
amount of sense.

Enjoy,
DoN.