Identifying Caps

[bluetubes]

Sorry if this has been posted before....I couldn't find an answer.  I just came across a pretty big pile of old capacitors.  Most are axial type and some are marked for polarity.  Some however are pretty low value (say....0.047µf or 0.0068µf) and marked with a black or grey band on one side.  Is there a rule for determining electrolytic Capactors?  How can I tell if a cap is polarized or not?

Thanks
BT

[aron]

Good question. I don't know. I didn't see anything in here:

http://www.repairfaq.org/sam/captest.htm#cttes

[petemoore]

  I suppose polarized caps without polarization markings exist, these markings can be vague, small and sometimes just a - toward one end to mark negative.
  I've not seen a polarized cap that had no polarity marking.
  The only way I've found to test caps is by doing swaps [a circuit is needed and a socket helps] and comparing to 'known good' good capacitors.
  Swapping out is an old time favorite test method.

[bluetubes]

Plug it in backwards, duck under the desk, cover my ears and flip the power on.     

Seriously though....how much am I risking by trying a cap (in both directions) in a circuit?  The are all ranges of voltages & some are up around 600v - 1000V.  I do have a small cap checker and I have tried some small electrolytics in both directions and the measurement was the same in both cases....so I guess that's out. 

Oh....that is a cool read Aron.   Gonna upgrade my cap drainer (two alligator clips and a 30K 10W resistor) with an LED!  Thanks.

[bluetubes]

I sorted out a small sample and took a quick pic.  Most have a layer of dust and grime, but most are unused.

http://s6.photobucket.com/albums/y230/Bluetubes/diy/?action=view&current=caps.jpg&refPage=&imgAnch=imgAnch1

[petemoore]

  all except the red and black ones to the left look polarized.
  The line across one end indicates the - pole.

[bluetubes]

That's what I was thinking....but I guess I'm just not used to seeing such small values in polarized caps.  It seems odd to me to have a 0.0068µf cap in polarized form.